diff --git a/README.md b/README.md
index 5dc8b5e..ff32c46 100644
--- a/README.md
+++ b/README.md
@@ -78,9 +78,12 @@ $newTable = $toSchema->createTable('new_table');
 
 // add columns
 $newTable->addColumn('id', 'integer', ['unsigned' => true]);
-$newTable->addColumn('payload', 'string');
+$newTable->addColumn('payload', 'string', ['notnull' => false]);
+// *option 'notnull' in false mode allows you to insert NULL into the column; 
+//                   in this case, the column will be represented in the ClickHouse as Nullable(String)
 $newTable->addColumn('hash', 'string', ['length' => 32, 'fixed' => true]);
-// *option 'fixed' sets the fixed length of a string column as specified; if specified, the type of the column is FixedString
+// *option 'fixed' sets the fixed length of a string column as specified; 
+//                 if specified, the type of the column is FixedString
 
 //set primary key
 $newTable->setPrimaryKey(['id']);
diff --git a/src/ClickHouseConnection.php b/src/ClickHouseConnection.php
index dbd54cc..15cd109 100644
--- a/src/ClickHouseConnection.php
+++ b/src/ClickHouseConnection.php
@@ -21,6 +21,8 @@
 use Doctrine\DBAL\Driver\ServerInfoAwareConnection;
 use Doctrine\DBAL\ParameterType;
 use Doctrine\DBAL\Platforms\AbstractPlatform;
+use function array_merge;
+use function func_get_args;
 
 /**
  * ClickHouse implementation for the Connection interface.
@@ -36,7 +38,7 @@ class ClickHouseConnection implements Connection, PingableConnection, ServerInfo
     /**
      * Connection constructor
      *
-     * @param array $params Array with connection params.
+     * @param mixed[] $params
      */
     public function __construct(
         array $params,
@@ -70,7 +72,7 @@ public function prepare($prepareString)
      */
     public function query()
     {
-        $args = \func_get_args();
+        $args = func_get_args();
         $stmt = $this->prepare($args[0]);
         $stmt->execute();
 
@@ -164,7 +166,7 @@ public function getServerVersion()
         try {
             return $this->smi2CHClient->getServerVersion();
         } catch (TransportException $exception) {
-            return null;
+            return '';
         }
     }
 
@@ -173,6 +175,6 @@ public function getServerVersion()
      */
     public function requiresQueryForServerVersion()
     {
-       return true;
+        return true;
     }
 }
diff --git a/src/ClickHousePlatform.php b/src/ClickHousePlatform.php
index e7a0d81..ea3c98b 100644
--- a/src/ClickHousePlatform.php
+++ b/src/ClickHousePlatform.php
@@ -14,19 +14,6 @@
 
 namespace FOD\DBALClickHouse;
 
-use Doctrine\DBAL\Types\{
-    BlobType,
-    DecimalType,
-    FloatType,
-    StringType,
-    TextType,
-    Type,
-    DateType,
-    IntegerType,
-    SmallIntType,
-    BigIntType,
-    DateTimeType
-};
 use Doctrine\DBAL\DBALException;
 use Doctrine\DBAL\ParameterType;
 use Doctrine\DBAL\Platforms\AbstractPlatform;
@@ -34,6 +21,37 @@
 use Doctrine\DBAL\Schema\ForeignKeyConstraint;
 use Doctrine\DBAL\Schema\Index;
 use Doctrine\DBAL\Schema\TableDiff;
+use Doctrine\DBAL\Types\BigIntType;
+use Doctrine\DBAL\Types\BlobType;
+use Doctrine\DBAL\Types\DateTimeType;
+use Doctrine\DBAL\Types\DateType;
+use Doctrine\DBAL\Types\DecimalType;
+use Doctrine\DBAL\Types\FloatType;
+use Doctrine\DBAL\Types\IntegerType;
+use Doctrine\DBAL\Types\SmallIntType;
+use Doctrine\DBAL\Types\StringType;
+use Doctrine\DBAL\Types\TextType;
+use Doctrine\DBAL\Types\Type;
+use FOD\DBALClickHouse\Types\BitNumericalClickHouseType;
+use FOD\DBALClickHouse\Types\DatableClickHouseType;
+use FOD\DBALClickHouse\Types\NumericalClickHouseType;
+use FOD\DBALClickHouse\Types\StringClickHouseType;
+use FOD\DBALClickHouse\Types\UnsignedNumericalClickHouseType;
+use function addslashes;
+use function array_filter;
+use function array_key_exists;
+use function array_keys;
+use function array_merge;
+use function array_unique;
+use function array_values;
+use function count;
+use function func_get_args;
+use function get_class;
+use function implode;
+use function in_array;
+use function sprintf;
+use function stripos;
+use function trim;
 
 /**
  * Provides the behavior, features and SQL dialect of the ClickHouse database platform.
@@ -50,7 +68,11 @@ class ClickHousePlatform extends AbstractPlatform
      */
     public function getBooleanTypeDeclarationSQL(array $columnDef) : string
     {
-        return 'UInt8';
+        return $this->prepareDeclarationSQL(
+            UnsignedNumericalClickHouseType::UNSIGNED_CHAR .
+            NumericalClickHouseType::TYPE_INT . BitNumericalClickHouseType::EIGHT_BIT,
+            $columnDef
+        );
     }
 
     /**
@@ -58,7 +80,11 @@ public function getBooleanTypeDeclarationSQL(array $columnDef) : string
      */
     public function getIntegerTypeDeclarationSQL(array $columnDef) : string
     {
-        return $this->_getCommonIntegerTypeDeclarationSQL($columnDef) . 'Int32';
+        return $this->prepareDeclarationSQL(
+            $this->_getCommonIntegerTypeDeclarationSQL($columnDef) .
+            NumericalClickHouseType::TYPE_INT . BitNumericalClickHouseType::THIRTY_TWO_BIT,
+            $columnDef
+        );
     }
 
     /**
@@ -66,7 +92,7 @@ public function getIntegerTypeDeclarationSQL(array $columnDef) : string
      */
     public function getBigIntTypeDeclarationSQL(array $columnDef) : string
     {
-        return 'String';
+        return $this->prepareDeclarationSQL(StringClickHouseType::TYPE_STRING, $columnDef);
     }
 
     /**
@@ -74,7 +100,11 @@ public function getBigIntTypeDeclarationSQL(array $columnDef) : string
      */
     public function getSmallIntTypeDeclarationSQL(array $columnDef) : string
     {
-        return $this->_getCommonIntegerTypeDeclarationSQL($columnDef) . 'Int16';
+        return $this->prepareDeclarationSQL(
+            $this->_getCommonIntegerTypeDeclarationSQL($columnDef) .
+            NumericalClickHouseType::TYPE_INT . BitNumericalClickHouseType::SIXTEEN_BIT,
+            $columnDef
+        );
     }
 
     /**
@@ -86,7 +116,7 @@ protected function _getCommonIntegerTypeDeclarationSQL(array $columnDef) : strin
             throw new \Exception('Clickhouse do not support AUTO_INCREMENT fields');
         }
 
-        return empty($columnDef['unsigned']) ? '' : 'U';
+        return empty($columnDef['unsigned']) ? '' : UnsignedNumericalClickHouseType::UNSIGNED_CHAR;
     }
 
     /**
@@ -128,6 +158,37 @@ protected function initializeDoctrineTypeMappings() : void
 
             'enum8' => 'string',
             'enum16' => 'string',
+
+            'nullable(int8)' => 'smallint',
+            'nullable(int16)' => 'integer',
+            'nullable(int32)' => 'integer',
+            'nullable(int64)' => 'bigint',
+            'nullable(uint8)' => 'smallint',
+            'nullable(uint16)' => 'integer',
+            'nullable(uint32)' => 'integer',
+            'nullable(uint64)' => 'bigint',
+            'nullable(float32)' => 'decimal',
+            'nullable(float64)' => 'float',
+
+            'nullable(string)' => 'string',
+            'nullable(fixedstring)' => 'string',
+            'nullable(date)' => 'date',
+            'nullable(datetime)' => 'datetime',
+
+            'array(nullable(int8))' => 'array',
+            'array(nullable(int16))' => 'array',
+            'array(nullable(int32))' => 'array',
+            'array(nullable(int64))' => 'array',
+            'array(nullable(uint8))' => 'array',
+            'array(nullable(uint16))' => 'array',
+            'array(nullable(uint32))' => 'array',
+            'array(nullable(uint64))' => 'array',
+            'array(nullable(float32))' => 'array',
+            'array(nullable(float64))' => 'array',
+
+            'array(nullable(string))' => 'array',
+            'array(nullable(date))' => 'array',
+            'array(nullable(datetime))' => 'array',
         ];
     }
 
@@ -137,8 +198,33 @@ protected function initializeDoctrineTypeMappings() : void
     protected function getVarcharTypeDeclarationSQLSnippet($length, $fixed) : string
     {
         return $fixed
-            ? 'FixedString(' . $length . ')'
-            : 'String';
+            ? (StringClickHouseType::TYPE_FIXED_STRING . '(' . $length . ')')
+            : StringClickHouseType::TYPE_STRING;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function getVarcharTypeDeclarationSQL(array $field)
+    {
+        if (! isset($field['length'])) {
+            $field['length'] = $this->getVarcharDefaultLength();
+        }
+
+        $fixed = $field['fixed'] ?? false;
+
+        $maxLength = $fixed
+            ? $this->getCharMaxLength()
+            : $this->getVarcharMaxLength();
+
+        if ($field['length'] > $maxLength) {
+            return $this->getClobTypeDeclarationSQL($field);
+        }
+
+        return $this->prepareDeclarationSQL(
+            $this->getVarcharTypeDeclarationSQLSnippet($field['length'], $fixed),
+            $field
+        );
     }
 
     /**
@@ -146,7 +232,7 @@ protected function getVarcharTypeDeclarationSQLSnippet($length, $fixed) : string
      */
     protected function getBinaryTypeDeclarationSQLSnippet($length, $fixed) : string
     {
-        return 'String';
+        return StringClickHouseType::TYPE_STRING;
     }
 
     /**
@@ -154,7 +240,7 @@ protected function getBinaryTypeDeclarationSQLSnippet($length, $fixed) : string
      */
     public function getClobTypeDeclarationSQL(array $field) : string
     {
-        return 'String';
+        return $this->prepareDeclarationSQL(StringClickHouseType::TYPE_STRING, $field);
     }
 
     /**
@@ -162,7 +248,7 @@ public function getClobTypeDeclarationSQL(array $field) : string
      */
     public function getBlobTypeDeclarationSQL(array $field) : string
     {
-        return 'String';
+        return $this->prepareDeclarationSQL(StringClickHouseType::TYPE_STRING, $field);
     }
 
     /**
@@ -323,7 +409,7 @@ public function getSubstringExpression($value, $from, $length = null) : string
      */
     public function getConcatExpression() : string
     {
-        return 'concat(' . implode(', ', \func_get_args()) . ')';
+        return 'concat(' . implode(', ', func_get_args()) . ')';
     }
 
     /**
@@ -331,7 +417,7 @@ public function getConcatExpression() : string
      */
     public function getIsNullExpression($expression)
     {
-        throw DBALException::notSupported(__METHOD__);
+        return 'isNull(' . $expression . ')';
     }
 
     /**
@@ -339,7 +425,7 @@ public function getIsNullExpression($expression)
      */
     public function getIsNotNullExpression($expression)
     {
-        throw DBALException::notSupported(__METHOD__);
+        return 'isNotNull(' . $expression . ')';
     }
 
     /**
@@ -561,7 +647,7 @@ protected function _getCreateTableSQL($tableName, array $columns, array $options
         /**
          * MergeTree* specific section
          */
-        if (\in_array(
+        if (in_array(
             $engine,
             [
                 'MergeTree',
@@ -639,7 +725,7 @@ protected function _getCreateTableSQL($tableName, array $columns, array $options
                     throw new \Exception(
                         'In table `' . $tableName . '` you have set field `' .
                         $options['eventDateColumn'] .
-                        '` (' . \get_class($columns[$options['eventDateColumn']]['type']) . ')
+                        '` (' . get_class($columns[$options['eventDateColumn']]['type']) . ')
                          as `eventDateColumn`, but it is not instance of DateType'
                     );
                 }
@@ -650,7 +736,8 @@ protected function _getCreateTableSQL($tableName, array $columns, array $options
                 $eventDateColumnName = $options['eventDateColumn'];
             }
             $dateColumnParams['name'] = $eventDateColumnName;
-            $columns                  = [$eventDateColumnName => $dateColumnParams] + $columns; // insert into very beginning
+            // insert into very beginning
+            $columns = [$eventDateColumnName => $dateColumnParams] + $columns;
 
             /**
              * Primary key section
@@ -682,8 +769,9 @@ protected function _getCreateTableSQL($tableName, array $columns, array $options
                     ! $columns[$options['versionColumn']]['type'] instanceof DateTimeType
                 ) {
                     throw new \Exception(
-                        'For ReplacingMergeTree tables `versionColumn` must be any of UInt* family, or Date, or DateTime types. ' .
-                        \get_class($columns[$options['versionColumn']]['type']) . ' given.'
+                        'For ReplacingMergeTree tables `versionColumn` must be any of UInt* family, 
+                        or Date, or DateTime types. ' .
+                        get_class($columns[$options['versionColumn']]['type']) . ' given.'
                     );
                 }
 
@@ -693,10 +781,13 @@ protected function _getCreateTableSQL($tableName, array $columns, array $options
             $engineOptions .= ')';
         }
 
-        $columnListSql = $this->getColumnDeclarationListSQL($columns);
-        $query         = 'CREATE TABLE ' . $tableName . ' (' . $columnListSql . ') ENGINE = ' . $engine . $engineOptions;
-
-        $sql[] = $query;
+        $sql[] = sprintf(
+            'CREATE TABLE %s (%s) ENGINE = %s%s',
+            $tableName,
+            $this->getColumnDeclarationListSQL($columns),
+            $engine,
+            $engineOptions
+        );
 
         return $sql;
     }
@@ -804,6 +895,18 @@ protected function _getAlterTableIndexForeignKeySQL(TableDiff $diff)
         throw DBALException::notSupported(__METHOD__);
     }
 
+    /**
+     * @param mixed[] $columnDef
+     */
+    protected function prepareDeclarationSQL(string $declarationSQL, array $columnDef) : string
+    {
+        if (array_key_exists('notnull', $columnDef) && $columnDef['notnull'] === false) {
+            return 'Nullable(' . $declarationSQL . ')';
+        }
+
+        return $declarationSQL;
+    }
+
     /**
      * {@inheritDoc}
      */
@@ -825,7 +928,7 @@ public function getColumnDeclarationSQL($name, array $field) : string
      */
     public function getDecimalTypeDeclarationSQL(array $columnDef) : string
     {
-        return 'String';
+        return $this->prepareDeclarationSQL(StringClickHouseType::TYPE_STRING, $columnDef);
     }
 
     /**
@@ -930,7 +1033,10 @@ public function getListDatabasesSQL() : string
      */
     public function getListTableColumnsSQL($table, $database = null) : string
     {
-        return 'DESCRIBE TABLE ' . ($database ? $this->quoteSingleIdentifier($database) . '.' : '') . $this->quoteSingleIdentifier($table);
+        return sprintf(
+            'DESCRIBE TABLE %s',
+            ($database ? $this->quoteSingleIdentifier($database) . '.' : '') . $this->quoteSingleIdentifier($table)
+        );
     }
 
     /**
@@ -978,7 +1084,7 @@ public function getCreateDatabaseSQL($database) : string
      */
     public function getDateTimeTypeDeclarationSQL(array $fieldDeclaration) : string
     {
-        return 'DateTime';
+        return $this->prepareDeclarationSQL(DatableClickHouseType::TYPE_DATE_TIME, $fieldDeclaration);
     }
 
     /**
@@ -986,12 +1092,15 @@ public function getDateTimeTypeDeclarationSQL(array $fieldDeclaration) : string
      */
     public function getDateTimeTzTypeDeclarationSQL(array $fieldDeclaration) : string
     {
-        return 'DateTime';
+        return $this->prepareDeclarationSQL(DatableClickHouseType::TYPE_DATE_TIME, $fieldDeclaration);
     }
 
+    /**
+     * {@inheritDoc}
+     */
     public function getTimeTypeDeclarationSQL(array $fieldDeclaration) : string
     {
-        return 'String';
+        return $this->prepareDeclarationSQL(StringClickHouseType::TYPE_STRING, $fieldDeclaration);
     }
 
     /**
@@ -999,7 +1108,7 @@ public function getTimeTypeDeclarationSQL(array $fieldDeclaration) : string
      */
     public function getDateTypeDeclarationSQL(array $fieldDeclaration) : string
     {
-        return 'Date';
+        return $this->prepareDeclarationSQL(DatableClickHouseType::TYPE_DATE, $fieldDeclaration);
     }
 
     /**
@@ -1007,7 +1116,10 @@ public function getDateTypeDeclarationSQL(array $fieldDeclaration) : string
      */
     public function getFloatDeclarationSQL(array $fieldDeclaration) : string
     {
-        return 'Float64';
+        return $this->prepareDeclarationSQL(
+            NumericalClickHouseType::TYPE_FLOAT . BitNumericalClickHouseType::SIXTY_FOUR_BIT,
+            $fieldDeclaration
+        );
     }
 
     /**
@@ -1141,23 +1253,30 @@ public function getDefaultValueDeclarationSQL($field) : string
         if (! isset($field['default'])) {
             return '';
         }
-
-        $default = " DEFAULT '" . $field['default'] . "'";
-        if ($fieldType = (string) ($field['type'] ?? null)) {
-            if (\in_array($fieldType, [
+        $defaultValue = $this->quoteStringLiteral($field['default']);
+        $fieldType    = $field['type'] ?: null;
+        if ($fieldType !== null) {
+            if ($fieldType === DatableClickHouseType::TYPE_DATE ||
+                $fieldType instanceof DateType ||
+                in_array($fieldType, [
                     'Integer',
                     'SmallInt',
                     'Float',
-                ]) || ($fieldType === 'BigInt' && Type::getType('BigInt')->getBindingType() === ParameterType::INTEGER)) {
-                $default = ' DEFAULT ' . $field['default'];
-            } elseif ($fieldType === 'DateTime' && $field['default'] === $this->getCurrentTimestampSQL()) {
-                $default = ' DEFAULT ' . $this->getCurrentTimestampSQL();
-            } elseif ($fieldType === 'Date') { // TODO check if string matches constant date like 'dddd-yy-mm' and quote it
-                $default = ' DEFAULT ' . $field['default'];
+                ]) ||
+                (
+                    $fieldType === 'BigInt'
+                    && Type::getType('BigInt')->getBindingType() === ParameterType::INTEGER
+                )
+            ) {
+                $defaultValue = $field['default'];
+            } elseif ($fieldType === DatableClickHouseType::TYPE_DATE_TIME &&
+                $field['default'] === $this->getCurrentTimestampSQL()
+            ) {
+                $defaultValue = $this->getCurrentTimestampSQL();
             }
         }
 
-        return $default;
+        return sprintf(' DEFAULT %s', $defaultValue);
     }
 
     /**
diff --git a/src/ClickHouseSchemaManager.php b/src/ClickHouseSchemaManager.php
index f3ba5d0..69cc2b4 100644
--- a/src/ClickHouseSchemaManager.php
+++ b/src/ClickHouseSchemaManager.php
@@ -18,6 +18,12 @@
 use Doctrine\DBAL\Schema\Column;
 use Doctrine\DBAL\Schema\View;
 use Doctrine\DBAL\Types\Type;
+use const CASE_LOWER;
+use function array_change_key_case;
+use function preg_replace;
+use function stripos;
+use function strtolower;
+use function trim;
 
 /**
  * Schema manager for the ClickHouse DBMS.
diff --git a/src/ClickHouseStatement.php b/src/ClickHouseStatement.php
index 516ed60..d9532be 100644
--- a/src/ClickHouseStatement.php
+++ b/src/ClickHouseStatement.php
@@ -19,6 +19,25 @@
 use Doctrine\DBAL\FetchMode;
 use Doctrine\DBAL\ParameterType;
 use Doctrine\DBAL\Platforms\AbstractPlatform;
+use function array_key_exists;
+use function array_keys;
+use function array_map;
+use function array_replace;
+use function array_shift;
+use function array_values;
+use function array_walk;
+use function count;
+use function current;
+use function explode;
+use function implode;
+use function in_array;
+use function is_array;
+use function is_bool;
+use function is_float;
+use function is_int;
+use function preg_replace;
+use function stripos;
+use function trim;
 
 /**
  * ClickHouse Statement
@@ -34,18 +53,18 @@ class ClickHouseStatement implements \IteratorAggregate, Statement
     /** @var AbstractPlatform */
     protected $platform;
 
-    /** @var array|null */
-    protected $rows;
+    /** @var mixed[] */
+    protected $rows = [];
 
     /**
      * Query parameters for prepared statement (key => value)
-     * @var array
+     * @var mixed[]
      */
     protected $values = [];
 
     /**
      * Query parameters' types for prepared statement (key => value)
-     * @var array
+     * @var mixed[]
      */
     protected $types = [];
 
@@ -68,7 +87,7 @@ public function __construct(Client $client, string $statement, AbstractPlatform
     public function getIterator() : \ArrayIterator
     {
         if (! $this->iterator) {
-            $this->iterator = new \ArrayIterator($this->rows ?: []);
+            $this->iterator = new \ArrayIterator($this->rows);
         }
 
         return $this->iterator;
@@ -79,7 +98,7 @@ public function getIterator() : \ArrayIterator
      */
     public function closeCursor()
     {
-        $this->rows     = null;
+        $this->rows     = [];
         $this->iterator = null;
 
         return true;
@@ -108,7 +127,7 @@ public function setFetchMode($fetchMode, $arg2 = null, $arg3 = null)
     protected function assumeFetchMode(?int $fetchMode = null) : int
     {
         $mode = $fetchMode ?: $this->fetchMode;
-        if (! \in_array($mode, [
+        if (! in_array($mode, [
             FetchMode::ASSOCIATIVE,
             FetchMode::NUMERIC,
             FetchMode::STANDARD_OBJECT,
@@ -147,7 +166,9 @@ public function fetch($fetchMode = null, $cursorOrientation = \PDO::FETCH_ORI_NE
 
         if ($this->assumeFetchMode($fetchMode) === \PDO::FETCH_KEY_PAIR) {
             if (count($data) < 2) {
-                throw new \Exception('To fetch in \PDO::FETCH_KEY_PAIR mode, result set must contain at least 2 columns');
+                throw new \Exception(
+                    'To fetch in \PDO::FETCH_KEY_PAIR mode, result set must contain at least 2 columns'
+                );
             }
 
             return [array_shift($data) => array_shift($data)];
@@ -190,7 +211,9 @@ function ($row) {
             return array_map(
                 function ($row) {
                     if (count($row) < 2) {
-                        throw new \Exception('To fetch in \PDO::FETCH_KEY_PAIR mode, result set must contain at least 2 columns');
+                        throw new \Exception(
+                            'To fetch in \PDO::FETCH_KEY_PAIR mode, result set must contain at least 2 columns'
+                        );
                     }
 
                     return [array_shift($row) => array_shift($row)];
@@ -207,7 +230,8 @@ function ($row) {
      */
     public function fetchColumn($columnIndex = 0)
     {
-        if ($elem = $this->fetch(FetchMode::NUMERIC)) {
+        $elem = $this->fetch(FetchMode::NUMERIC);
+        if (is_array($elem)) {
             return $elem[$columnIndex] ?? $elem[0];
         }
 
@@ -248,7 +272,7 @@ public function errorInfo() : void
     public function execute($params = null) : bool
     {
         $hasZeroIndex = false;
-        if (\is_array($params)) {
+        if (is_array($params)) {
             $this->values = array_replace($this->values, $params);//TODO array keys must be all strings or all integers?
             $hasZeroIndex = array_key_exists(0, $params);
         }
@@ -268,7 +292,7 @@ public function execute($params = null) : bool
         } else {
             foreach (array_keys($this->values) as $key) {
                 $sql = preg_replace(
-                    '/(' . (\is_int($key) ? '\?' : ':' . $key) . ')/i',
+                    '/(' . (is_int($key) ? '\?' : ':' . $key) . ')/i',
                     $this->getTypedParam($key),
                     $sql,
                     1
@@ -317,40 +341,44 @@ protected function processViaSMI2(string $sql) : void
      */
     protected function getTypedParam($key) : string
     {
+        if ($this->values[$key] === null) {
+            return 'NULL';
+        }
+
         $type = $this->types[$key] ?? null;
 
         // if param type was not setted - trying to get db-type by php-var-type
         if ($type === null) {
-            if (\is_bool($this->values[$key])) {
+            if (is_bool($this->values[$key])) {
                 $type = ParameterType::BOOLEAN;
-            } elseif (\is_int($this->values[$key]) || \is_float($this->values[$key])) {
+            } elseif (is_int($this->values[$key]) || is_float($this->values[$key])) {
                 $type = ParameterType::INTEGER;
-            } elseif (\is_array($this->values[$key])) {
+            } elseif (is_array($this->values[$key])) {
                 /*
                  * ClickHouse Arrays
                  */
                 $values = $this->values[$key];
-                if (\is_int(current($values)) || \is_float(current($values))) {
+                if (is_int(current($values)) || is_float(current($values))) {
                     array_map(
                         function ($value) : void {
-                            if (! \is_int($value) && ! \is_float($value)) {
-                                throw new ClickHouseException('Array values must all be int/float or string, mixes not allowed');
+                            if (! is_int($value) && ! is_float($value)) {
+                                throw new ClickHouseException(
+                                    'Array values must all be int/float or string, mixes not allowed'
+                                );
                             }
                         },
                         $values
                     );
                 } else {
-                    $values = array_map([$this->platform, 'quoteStringLiteral'], $values);
+                    $values = array_map(function ($value) {
+                        return $value === null ? 'NULL' : $this->platform->quoteStringLiteral($value);
+                    }, $values);
                 }
 
                 return '[' . implode(', ', $values) . ']';
             }
         }
 
-        if ($type === ParameterType::NULL) {
-            throw new ClickHouseException('NULLs are not supported by ClickHouse');
-        }
-
         if ($type === ParameterType::INTEGER) {
             return (string) $this->values[$key];
         }
diff --git a/src/Connection.php b/src/Connection.php
index 35bfdaa..80f8e72 100644
--- a/src/Connection.php
+++ b/src/Connection.php
@@ -15,6 +15,9 @@
 namespace FOD\DBALClickHouse;
 
 use Doctrine\DBAL\DBALException;
+use function strtoupper;
+use function substr;
+use function trim;
 
 /**
  * ClickHouse Connection
diff --git a/src/Types/AbstractArrayFloatType.php b/src/Types/AbstractArrayFloatType.php
deleted file mode 100644
index 88f2970..0000000
--- a/src/Types/AbstractArrayFloatType.php
+++ /dev/null
@@ -1,39 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-/*
- * This file is part of the FODDBALClickHouse package -- Doctrine DBAL library
- * for ClickHouse (a column-oriented DBMS for OLAP <https://clickhouse.yandex/>)
- *
- * (c) FriendsOfDoctrine <https://github.com/FriendsOfDoctrine/>.
- *
- * For the full copyright and license inflormation, please view the LICENSE
- * file that was distributed with this source code.
- */
-
-namespace FOD\DBALClickHouse\Types;
-
-use Doctrine\DBAL\Platforms\AbstractPlatform;
-
-/**
- * Array(Float*) Types basic class
- */
-abstract class AbstractArrayFloatType extends AbstractArrayNumType
-{
-    /**
-     * {@inheritDoc}
-     */
-    public function getSQLDeclaration(array $fieldDeclaration, AbstractPlatform $platform) : string
-    {
-        return 'Array(Float' . $this->getBitness() . ')';
-    }
-
-    /**
-     * {@inheritDoc}
-     */
-    public function getName() : string
-    {
-        return 'array(float' . $this->getBitness() . ')';
-    }
-}
diff --git a/src/Types/AbstractArrayIntType.php b/src/Types/AbstractArrayIntType.php
deleted file mode 100644
index 06d3b55..0000000
--- a/src/Types/AbstractArrayIntType.php
+++ /dev/null
@@ -1,41 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-/*
- * This file is part of the FODDBALClickHouse package -- Doctrine DBAL library
- * for ClickHouse (a column-oriented DBMS for OLAP <https://clickhouse.yandex/>)
- *
- * (c) FriendsOfDoctrine <https://github.com/FriendsOfDoctrine/>.
- *
- * For the full copyright and license inflormation, please view the LICENSE
- * file that was distributed with this source code.
- */
-
-namespace FOD\DBALClickHouse\Types;
-
-use Doctrine\DBAL\Platforms\AbstractPlatform;
-
-/**
- * Array(Int*) Types basic class
- */
-abstract class AbstractArrayIntType extends AbstractArrayNumType
-{
-    public const UNSIGNED = false;
-
-    /**
-     * {@inheritDoc}
-     */
-    public function getSQLDeclaration(array $fieldDeclaration, AbstractPlatform $platform) : string
-    {
-        return 'Array(' . (static::UNSIGNED ? 'U' : '') . 'Int' . $this->getBitness() . ')';
-    }
-
-    /**
-     * {@inheritDoc}
-     */
-    public function getName() : string
-    {
-        return 'array(' . (static::UNSIGNED ? 'u' : '') . 'int' . $this->getBitness() . ')';
-    }
-}
diff --git a/src/Types/ArrayDateTimeType.php b/src/Types/ArrayDateTimeType.php
index d7daffa..76cf715 100644
--- a/src/Types/ArrayDateTimeType.php
+++ b/src/Types/ArrayDateTimeType.php
@@ -16,26 +16,18 @@
 
 use Doctrine\DBAL\ParameterType;
 use Doctrine\DBAL\Platforms\AbstractPlatform;
+use function array_filter;
+use function array_map;
+use function implode;
 
 /**
  * Array(DateTime) Type class
  */
-class ArrayDateTimeType extends AbstractArrayType
+class ArrayDateTimeType extends ArrayType implements DatableClickHouseType
 {
-    /**
-     * {@inheritDoc}
-     */
-    public function getSQLDeclaration(array $fieldDeclaration, AbstractPlatform $platform) : string
-    {
-        return 'Array(DateTime)';
-    }
-
-    /**
-     * {@inheritDoc}
-     */
-    public function getName() : string
+    public function getBaseClickHouseType() : string
     {
-        return 'array(datetime)';
+        return DatableClickHouseType::TYPE_DATE_TIME;
     }
 
     /**
@@ -43,9 +35,12 @@ public function getName() : string
      */
     public function convertToPHPValue($value, AbstractPlatform $platform)
     {
-        return array_map(function ($stringDatetime) use ($platform) {
-            return \DateTime::createFromFormat($platform->getDateTimeFormatString(), $stringDatetime);
-        }, (array) $value);
+        return array_map(
+            function ($stringDatetime) use ($platform) {
+                return \DateTime::createFromFormat($platform->getDateTimeFormatString(), $stringDatetime);
+            },
+            (array) $value
+        );
     }
 
     /**
@@ -55,11 +50,17 @@ public function convertToDatabaseValue($value, AbstractPlatform $platform)
     {
         return '[' . implode(
             ', ',
-            array_map(function (\DateTime $datetime) use ($platform) {
+            array_map(
+                function (\DateTime $datetime) use ($platform) {
                     return "'" . $datetime->format($platform->getDateTimeFormatString()) . "'";
-            }, array_filter((array) $value, function ($datetime) {
-                return $datetime instanceof \DateTime;
-            }))
+                },
+                array_filter(
+                    (array) $value,
+                    function ($datetime) {
+                        return $datetime instanceof \DateTime;
+                    }
+                )
+            )
         ) . ']';
     }
 
diff --git a/src/Types/ArrayDateType.php b/src/Types/ArrayDateType.php
index e546cbd..f96829d 100644
--- a/src/Types/ArrayDateType.php
+++ b/src/Types/ArrayDateType.php
@@ -16,26 +16,18 @@
 
 use Doctrine\DBAL\ParameterType;
 use Doctrine\DBAL\Platforms\AbstractPlatform;
+use function array_filter;
+use function array_map;
+use function implode;
 
 /**
  * Array(Date) Type class
  */
-class ArrayDateType extends AbstractArrayType
+class ArrayDateType extends ArrayType implements DatableClickHouseType
 {
-    /**
-     * {@inheritDoc}
-     */
-    public function getSQLDeclaration(array $fieldDeclaration, AbstractPlatform $platform) : string
-    {
-        return 'Array(Date)';
-    }
-
-    /**
-     * {@inheritDoc}
-     */
-    public function getName() : string
+    public function getBaseClickHouseType() : string
     {
-        return 'array(date)';
+        return DatableClickHouseType::TYPE_DATE;
     }
 
     /**
@@ -43,9 +35,12 @@ public function getName() : string
      */
     public function convertToPHPValue($value, AbstractPlatform $platform)
     {
-        return array_map(function ($stringDatetime) use ($platform) {
-            return \DateTime::createFromFormat($platform->getDateFormatString(), $stringDatetime);
-        }, (array) $value);
+        return array_map(
+            function ($stringDatetime) use ($platform) {
+                return \DateTime::createFromFormat($platform->getDateFormatString(), $stringDatetime);
+            },
+            (array) $value
+        );
     }
 
     /**
@@ -55,11 +50,17 @@ public function convertToDatabaseValue($value, AbstractPlatform $platform)
     {
         return '[' . implode(
             ', ',
-            array_map(function (\DateTime $datetime) use ($platform) {
+            array_map(
+                function (\DateTime $datetime) use ($platform) {
                     return "'" . $datetime->format($platform->getDateFormatString()) . "'";
-            }, array_filter((array) $value, function ($datetime) {
-                return $datetime instanceof \DateTime;
-            }))
+                },
+                array_filter(
+                    (array) $value,
+                    function ($datetime) {
+                        return $datetime instanceof \DateTime;
+                    }
+                )
+            )
         ) . ']';
     }
 
diff --git a/src/Types/ArrayFloat32Type.php b/src/Types/ArrayFloat32Type.php
index c5e4467..fcc0b27 100644
--- a/src/Types/ArrayFloat32Type.php
+++ b/src/Types/ArrayFloat32Type.php
@@ -17,13 +17,15 @@
 /**
  * Array(Float32) Type
  */
-class ArrayFloat32Type extends AbstractArrayFloatType
+class ArrayFloat32Type extends ArrayType implements BitNumericalClickHouseType
 {
-    public const BITNESS = 32;
+    public function getBits() : int
+    {
+        return BitNumericalClickHouseType::THIRTY_TWO_BIT;
+    }
 
-    /** {@inheritdoc} */
-    protected function getBitness() : int
+    public function getBaseClickHouseType() : string
     {
-        return self::BITNESS;
+        return NumericalClickHouseType::TYPE_FLOAT;
     }
 }
diff --git a/src/Types/ArrayFloat64Type.php b/src/Types/ArrayFloat64Type.php
index f51ee29..01c8790 100644
--- a/src/Types/ArrayFloat64Type.php
+++ b/src/Types/ArrayFloat64Type.php
@@ -17,13 +17,15 @@
 /**
  * Array(Float64) Type
  */
-class ArrayFloat64Type extends AbstractArrayFloatType
+class ArrayFloat64Type extends ArrayType implements BitNumericalClickHouseType
 {
-    public const BITNESS = 64;
+    public function getBits() : int
+    {
+        return BitNumericalClickHouseType::SIXTY_FOUR_BIT;
+    }
 
-    /** {@inheritdoc} */
-    protected function getBitness() : int
+    public function getBaseClickHouseType() : string
     {
-        return self::BITNESS;
+        return NumericalClickHouseType::TYPE_FLOAT;
     }
 }
diff --git a/src/Types/ArrayInt16Type.php b/src/Types/ArrayInt16Type.php
index 034563a..0c78d76 100644
--- a/src/Types/ArrayInt16Type.php
+++ b/src/Types/ArrayInt16Type.php
@@ -17,13 +17,15 @@
 /**
  * Array(Int16) Type
  */
-class ArrayInt16Type extends AbstractArrayIntType
+class ArrayInt16Type extends ArrayType implements BitNumericalClickHouseType
 {
-    public const BITNESS = 16;
+    public function getBits() : int
+    {
+        return BitNumericalClickHouseType::SIXTEEN_BIT;
+    }
 
-    /** {@inheritdoc} */
-    protected function getBitness() : int
+    public function getBaseClickHouseType() : string
     {
-        return self::BITNESS;
+        return NumericalClickHouseType::TYPE_INT;
     }
 }
diff --git a/src/Types/ArrayInt32Type.php b/src/Types/ArrayInt32Type.php
index 81a74a6..201278e 100644
--- a/src/Types/ArrayInt32Type.php
+++ b/src/Types/ArrayInt32Type.php
@@ -17,13 +17,15 @@
 /**
  * Array(Int32) Type
  */
-class ArrayInt32Type extends AbstractArrayIntType
+class ArrayInt32Type extends ArrayType implements BitNumericalClickHouseType
 {
-    public const BITNESS = 32;
+    public function getBits() : int
+    {
+        return BitNumericalClickHouseType::THIRTY_TWO_BIT;
+    }
 
-    /** {@inheritdoc} */
-    protected function getBitness() : int
+    public function getBaseClickHouseType() : string
     {
-        return self::BITNESS;
+        return NumericalClickHouseType::TYPE_INT;
     }
 }
diff --git a/src/Types/ArrayInt64Type.php b/src/Types/ArrayInt64Type.php
index 863cb4d..2e1860d 100644
--- a/src/Types/ArrayInt64Type.php
+++ b/src/Types/ArrayInt64Type.php
@@ -17,13 +17,15 @@
 /**
  * Array(Int64) Type
  */
-class ArrayInt64Type extends AbstractArrayIntType
+class ArrayInt64Type extends ArrayType implements BitNumericalClickHouseType
 {
-    public const BITNESS = 64;
+    public function getBits() : int
+    {
+        return BitNumericalClickHouseType::SIXTY_FOUR_BIT;
+    }
 
-    /** {@inheritdoc} */
-    protected function getBitness() : int
+    public function getBaseClickHouseType() : string
     {
-        return self::BITNESS;
+        return NumericalClickHouseType::TYPE_INT;
     }
 }
diff --git a/src/Types/ArrayInt8Type.php b/src/Types/ArrayInt8Type.php
index 8099a9d..9f18e6f 100644
--- a/src/Types/ArrayInt8Type.php
+++ b/src/Types/ArrayInt8Type.php
@@ -17,13 +17,15 @@
 /**
  * Array(Int8) Type
  */
-class ArrayInt8Type extends AbstractArrayIntType
+class ArrayInt8Type extends ArrayType implements BitNumericalClickHouseType
 {
-    public const BITNESS = 8;
+    public function getBits() : int
+    {
+        return BitNumericalClickHouseType::EIGHT_BIT;
+    }
 
-    /** {@inheritdoc} */
-    protected function getBitness() : int
+    public function getBaseClickHouseType() : string
     {
-        return self::BITNESS;
+        return NumericalClickHouseType::TYPE_INT;
     }
 }
diff --git a/src/Types/ArrayStringType.php b/src/Types/ArrayStringType.php
index 64cb5c6..8b39e5f 100644
--- a/src/Types/ArrayStringType.php
+++ b/src/Types/ArrayStringType.php
@@ -16,26 +16,17 @@
 
 use Doctrine\DBAL\ParameterType;
 use Doctrine\DBAL\Platforms\AbstractPlatform;
+use function array_map;
+use function implode;
 
 /**
  * Array(String) Type class
  */
-class ArrayStringType extends AbstractArrayType
+class ArrayStringType extends ArrayType implements StringClickHouseType
 {
-    /**
-     * {@inheritDoc}
-     */
-    public function getSQLDeclaration(array $fieldDeclaration, AbstractPlatform $platform) : string
-    {
-        return 'Array(String)';
-    }
-
-    /**
-     * {@inheritDoc}
-     */
-    public function getName() : string
+    public function getBaseClickHouseType() : string
     {
-        return 'array(string)';
+        return StringClickHouseType::TYPE_STRING;
     }
 
     /**
diff --git a/src/Types/AbstractArrayType.php b/src/Types/ArrayType.php
similarity index 64%
rename from src/Types/AbstractArrayType.php
rename to src/Types/ArrayType.php
index dd19594..2c185fc 100644
--- a/src/Types/AbstractArrayType.php
+++ b/src/Types/ArrayType.php
@@ -17,13 +17,16 @@
 use Doctrine\DBAL\DBALException;
 use Doctrine\DBAL\Platforms\AbstractPlatform;
 use Doctrine\DBAL\Types\Type;
+use function array_key_exists;
+use function sprintf;
+use function strtolower;
 
 /**
  * Array(*) Types basic class
  */
-abstract class AbstractArrayType extends Type
+abstract class ArrayType extends Type implements ClickHouseType
 {
-    public const ARRAY_TYPES = [
+    protected const ARRAY_TYPES = [
         'array(int8)' => ArrayInt8Type::class,
         'array(int16)' => ArrayInt16Type::class,
         'array(int32)' => ArrayInt32Type::class,
@@ -65,4 +68,36 @@ public function getMappedDatabaseTypes(AbstractPlatform $platform) : array
     {
         return [$this->getName()];
     }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function getSQLDeclaration(array $fieldDeclaration, AbstractPlatform $platform) : string
+    {
+        return $this->getDeclaration($fieldDeclaration);
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function getName() : string
+    {
+        return strtolower($this->getDeclaration());
+    }
+
+    /**
+     * @param mixed[] $fieldDeclaration
+     */
+    protected function getDeclaration(array $fieldDeclaration = []) : string
+    {
+        return sprintf(
+            array_key_exists(
+                'notnull',
+                $fieldDeclaration
+            ) && $fieldDeclaration['notnull'] === false ? 'Array(Nullable(%s%s%s))' : 'Array(%s%s%s)',
+            $this instanceof UnsignedNumericalClickHouseType ? 'U' : '',
+            $this->getBaseClickHouseType(),
+            $this instanceof BitNumericalClickHouseType ? $this->getBits() : ''
+        );
+    }
 }
diff --git a/src/Types/ArrayUInt16Type.php b/src/Types/ArrayUInt16Type.php
index 98c2847..3fb8d4c 100644
--- a/src/Types/ArrayUInt16Type.php
+++ b/src/Types/ArrayUInt16Type.php
@@ -17,7 +17,15 @@
 /**
  * Array(UInt16) Type
  */
-class ArrayUInt16Type extends ArrayInt16Type
+class ArrayUInt16Type extends ArrayType implements BitNumericalClickHouseType, UnsignedNumericalClickHouseType
 {
-    public const UNSIGNED = true;
+    public function getBits() : int
+    {
+        return BitNumericalClickHouseType::SIXTEEN_BIT;
+    }
+
+    public function getBaseClickHouseType() : string
+    {
+        return NumericalClickHouseType::TYPE_INT;
+    }
 }
diff --git a/src/Types/ArrayUInt32Type.php b/src/Types/ArrayUInt32Type.php
index 39bec16..ef6794c 100644
--- a/src/Types/ArrayUInt32Type.php
+++ b/src/Types/ArrayUInt32Type.php
@@ -17,7 +17,15 @@
 /**
  * Array(UInt32) Type
  */
-class ArrayUInt32Type extends ArrayInt32Type
+class ArrayUInt32Type extends ArrayType implements BitNumericalClickHouseType, UnsignedNumericalClickHouseType
 {
-    public const UNSIGNED = true;
+    public function getBits() : int
+    {
+        return BitNumericalClickHouseType::THIRTY_TWO_BIT;
+    }
+
+    public function getBaseClickHouseType() : string
+    {
+        return NumericalClickHouseType::TYPE_INT;
+    }
 }
diff --git a/src/Types/ArrayUInt64Type.php b/src/Types/ArrayUInt64Type.php
index 5c42123..a21c280 100644
--- a/src/Types/ArrayUInt64Type.php
+++ b/src/Types/ArrayUInt64Type.php
@@ -17,7 +17,15 @@
 /**
  * Array(UInt64) Type
  */
-class ArrayUInt64Type extends ArrayInt64Type
+class ArrayUInt64Type extends ArrayType implements BitNumericalClickHouseType, UnsignedNumericalClickHouseType
 {
-    public const UNSIGNED = true;
+    public function getBits() : int
+    {
+        return BitNumericalClickHouseType::SIXTY_FOUR_BIT;
+    }
+
+    public function getBaseClickHouseType() : string
+    {
+        return NumericalClickHouseType::TYPE_INT;
+    }
 }
diff --git a/src/Types/ArrayUInt8Type.php b/src/Types/ArrayUInt8Type.php
index 832e886..626eafa 100644
--- a/src/Types/ArrayUInt8Type.php
+++ b/src/Types/ArrayUInt8Type.php
@@ -17,7 +17,15 @@
 /**
  * Array(UInt8) Type
  */
-class ArrayUInt8Type extends ArrayInt8Type
+class ArrayUInt8Type extends ArrayType implements BitNumericalClickHouseType, UnsignedNumericalClickHouseType
 {
-    public const UNSIGNED = true;
+    public function getBits() : int
+    {
+        return BitNumericalClickHouseType::EIGHT_BIT;
+    }
+
+    public function getBaseClickHouseType() : string
+    {
+        return NumericalClickHouseType::TYPE_INT;
+    }
 }
diff --git a/src/Types/AbstractArrayNumType.php b/src/Types/BitNumericalClickHouseType.php
similarity index 61%
rename from src/Types/AbstractArrayNumType.php
rename to src/Types/BitNumericalClickHouseType.php
index 0d412f2..ab843b8 100644
--- a/src/Types/AbstractArrayNumType.php
+++ b/src/Types/BitNumericalClickHouseType.php
@@ -14,13 +14,12 @@
 
 namespace FOD\DBALClickHouse\Types;
 
-/**
- * Array(Numeric) Types basic class
- */
-abstract class AbstractArrayNumType extends AbstractArrayType
+interface BitNumericalClickHouseType extends NumericalClickHouseType
 {
-    /**
-     * @return int Bitness of integers or floats in Array (Array(Int{bitness}) or Array(Float{bitness}))
-     */
-    abstract protected function getBitness() : int;
+    public const EIGHT_BIT      = 8;
+    public const SIXTEEN_BIT    = 16;
+    public const THIRTY_TWO_BIT = 32;
+    public const SIXTY_FOUR_BIT = 64;
+
+    public function getBits() : int;
 }
diff --git a/src/Types/ClickHouseType.php b/src/Types/ClickHouseType.php
new file mode 100644
index 0000000..9f12543
--- /dev/null
+++ b/src/Types/ClickHouseType.php
@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * This file is part of the FODDBALClickHouse package -- Doctrine DBAL library
+ * for ClickHouse (a column-oriented DBMS for OLAP <https://clickhouse.yandex/>)
+ *
+ * (c) FriendsOfDoctrine <https://github.com/FriendsOfDoctrine/>.
+ *
+ * For the full copyright and license inflormation, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace FOD\DBALClickHouse\Types;
+
+interface ClickHouseType
+{
+    public function getBaseClickHouseType() : string;
+}
diff --git a/src/Types/DatableClickHouseType.php b/src/Types/DatableClickHouseType.php
new file mode 100644
index 0000000..e2e7e5a
--- /dev/null
+++ b/src/Types/DatableClickHouseType.php
@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * This file is part of the FODDBALClickHouse package -- Doctrine DBAL library
+ * for ClickHouse (a column-oriented DBMS for OLAP <https://clickhouse.yandex/>)
+ *
+ * (c) FriendsOfDoctrine <https://github.com/FriendsOfDoctrine/>.
+ *
+ * For the full copyright and license inflormation, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace FOD\DBALClickHouse\Types;
+
+interface DatableClickHouseType extends ClickHouseType
+{
+    public const TYPE_DATE      = 'Date';
+    public const TYPE_DATE_TIME = 'DateTime';
+}
diff --git a/src/Types/NumericalClickHouseType.php b/src/Types/NumericalClickHouseType.php
new file mode 100644
index 0000000..ebee8ed
--- /dev/null
+++ b/src/Types/NumericalClickHouseType.php
@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * This file is part of the FODDBALClickHouse package -- Doctrine DBAL library
+ * for ClickHouse (a column-oriented DBMS for OLAP <https://clickhouse.yandex/>)
+ *
+ * (c) FriendsOfDoctrine <https://github.com/FriendsOfDoctrine/>.
+ *
+ * For the full copyright and license inflormation, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace FOD\DBALClickHouse\Types;
+
+interface NumericalClickHouseType extends ClickHouseType
+{
+    public const TYPE_INT   = 'Int';
+    public const TYPE_FLOAT = 'Float';
+}
diff --git a/src/Types/StringClickHouseType.php b/src/Types/StringClickHouseType.php
new file mode 100644
index 0000000..524d7e9
--- /dev/null
+++ b/src/Types/StringClickHouseType.php
@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * This file is part of the FODDBALClickHouse package -- Doctrine DBAL library
+ * for ClickHouse (a column-oriented DBMS for OLAP <https://clickhouse.yandex/>)
+ *
+ * (c) FriendsOfDoctrine <https://github.com/FriendsOfDoctrine/>.
+ *
+ * For the full copyright and license inflormation, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace FOD\DBALClickHouse\Types;
+
+interface StringClickHouseType extends ClickHouseType
+{
+    public const TYPE_STRING       = 'String';
+    public const TYPE_FIXED_STRING = 'FixedString';
+}
diff --git a/src/Types/UnsignedNumericalClickHouseType.php b/src/Types/UnsignedNumericalClickHouseType.php
new file mode 100644
index 0000000..f17132e
--- /dev/null
+++ b/src/Types/UnsignedNumericalClickHouseType.php
@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * This file is part of the FODDBALClickHouse package -- Doctrine DBAL library
+ * for ClickHouse (a column-oriented DBMS for OLAP <https://clickhouse.yandex/>)
+ *
+ * (c) FriendsOfDoctrine <https://github.com/FriendsOfDoctrine/>.
+ *
+ * For the full copyright and license inflormation, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace FOD\DBALClickHouse\Types;
+
+interface UnsignedNumericalClickHouseType extends NumericalClickHouseType
+{
+    public const UNSIGNED_CHAR = 'U';
+}
diff --git a/tests/ArraysTest.php b/tests/ArraysTest.php
index fb0225e..dfc412d 100644
--- a/tests/ArraysTest.php
+++ b/tests/ArraysTest.php
@@ -12,7 +12,7 @@
 namespace FOD\DBALClickHouse\Tests;
 
 use FOD\DBALClickHouse\Connection;
-use FOD\DBALClickHouse\Types\AbstractArrayType;
+use FOD\DBALClickHouse\Types\ArrayType;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -28,7 +28,7 @@ class ArraysTest extends TestCase
     public function setUp()
     {
         $this->connection = CreateConnectionTest::createConnection();
-        AbstractArrayType::registerArrayTypes($this->connection->getDatabasePlatform());
+        ArrayType::registerArrayTypes($this->connection->getDatabasePlatform());
     }
 
     public function tearDown()
diff --git a/tests/ConnectionTest.php b/tests/ConnectionTest.php
index 63bd06d..5603b10 100644
--- a/tests/ConnectionTest.php
+++ b/tests/ConnectionTest.php
@@ -150,7 +150,7 @@ public function testGetServerVersion()
     {
         $conn = $this->connection->getWrappedConnection();
         if ($conn instanceof ServerInfoAwareConnection) {
-            $this->assertRegExp('/(^[0-9]+.[0-9]+.[0-9]+.[0-9]$)/mi', $conn->getServerVersion());
+            $this->assertRegExp('/(^[0-9]+.[0-9]+.[0-9]+(.[0-9]$|$))/mi', $conn->getServerVersion());
         } else {
             $this->fail(sprintf('`%s` does not implement the `%s` interface', \get_class($conn),
                 ServerInfoAwareConnection::class));
diff --git a/tests/CreateSchemaTest.php b/tests/CreateSchemaTest.php
index 59dbaa5..3b3ad5e 100644
--- a/tests/CreateSchemaTest.php
+++ b/tests/CreateSchemaTest.php
@@ -15,6 +15,7 @@
 use Doctrine\DBAL\Types\Type;
 use FOD\DBALClickHouse\ClickHouseSchemaManager;
 use FOD\DBALClickHouse\Connection;
+use FOD\DBALClickHouse\Types\ArrayType;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -238,4 +239,75 @@ public function testEventDateProviderColumnBadOption()
         }
         $this->connection->exec('DROP TABLE test_table');
     }
+
+    public function testNullableColumns()
+    {
+        $fromSchema = $this->connection->getSchemaManager()->createSchema();
+        ArrayType::registerArrayTypes($this->connection->getDatabasePlatform());
+
+        $toSchema = clone $fromSchema;
+
+        $newTable = $toSchema->createTable('test_table_nullable');
+
+        $newTable->addColumn('id', 'integer', ['unsigned' => true, 'notnull' => false]);
+        $newTable->addColumn('payload', 'string', ['notnull' => false]);
+        $newTable->addColumn('price', 'float', ['notnull' => false]);
+        $newTable->addColumn('transactions', 'array(datetime)', ['notnull' => false]);
+        $newTable->addColumn('status', 'boolean', ['notnull' => false]);
+        $newTable->setPrimaryKey(['id']);
+        $newTable->addOption('engine', 'Memory');
+
+        $migrationSQLs = $fromSchema->getMigrateToSql($toSchema, $this->connection->getDatabasePlatform());
+        $generatedSQL = implode(';', $migrationSQLs);
+        $this->assertEquals("CREATE TABLE test_table_nullable (id UInt32, payload Nullable(String), price Nullable(Float64), transactions Array(Nullable(DateTime)), status Nullable(UInt8)) ENGINE = Memory",
+            $generatedSQL);
+        foreach ($migrationSQLs as $sql) {
+            $this->connection->exec($sql);
+        }
+        $this->connection->insert('test_table_nullable',
+            [
+                'id' => 1,
+                'payload' => 's1',
+                'price' => 1.5,
+                'transactions' => [date('Y-m-d H:i:s'), null],
+                'status' => null
+            ]);
+        $this->connection->insert('test_table_nullable',
+            [
+                'id' => 2,
+                'payload' => 's2',
+                'price' => 120,
+                'transactions' => [null, null],
+                'status' => false
+            ]);
+        $this->connection->insert('test_table_nullable',
+            [
+                'id' => 3,
+                'payload' => null,
+                'price' => 1000,
+                'transactions' => [date('Y-m-d H:i:s')],
+                'status' => true
+            ]);
+        $this->connection->insert('test_table_nullable',
+            [
+                'id' => 4,
+                'payload' => 's4',
+                'price' => null,
+                'transactions' => [date('Y-m-d H:i:s'), date('Y-m-d H:i:s')],
+                'status' => null
+            ]);
+        $this->connection->insert('test_table_nullable',
+            [
+                'id' => 5,
+                'payload' => 's5',
+                'price' => 100,
+                'transactions' => [date('Y-m-d H:i:s')],
+                'status' => true
+            ]);
+
+        $this->assertEquals(2,
+            (int)$this->connection->fetchColumn("SELECT count() from test_table_nullable WHERE {$this->connection->getDatabasePlatform()->getIsNullExpression('status')}"));
+
+        $this->connection->exec('DROP TABLE test_table_nullable');
+    }
 }