Improve null value validation (#126)

* Improve null value validation

* Corrected test-data path for the `a null property value should not cause an exception` test.

* Add changelog for null value validation

CHANGELOG.md

@@ -9,6 +9,7 @@ Versioning](http://semver.org/spec/v2.0.0.html).
 ### Fixed
 - Merge PR #120, fixing dependency issue with "@types/colors"
 - Merge PR #127, implementing "safer-buffer" polyfill to be compatible with older NodeJS versions
+- Merge PR #126, improving null value validation when null is passed into a template
 
 ## [1.5.1] - 2018-03-12
 ### Added

src/test/validatorTest.ts

@@ -732,7 +732,15 @@ describe('validator', () => {
             let result = validator.validateFile(input);
             expect(result).to.have.deep.property('templateValid', true);
             expect(result['errors']['crit']).to.have.lengthOf(0);
-        })
+        });
+
+        it('a null property value should not cause an exception', () => {
+            const input = 'testData/invalid/yaml/null_value.yaml';
+            let result = validator.validateFile(input);
+            expect(result).to.have.deep.property('templateValid', false);
+            expect(result['errors']['crit']).to.have.lengthOf(1);
+            expect(result['errors']['crit'][0]).to.have.property('message', 'Expecting a list, got null');
+        });
     });
 
     describe('parameters-validation', () => {

src/validator.ts

@@ -474,7 +474,7 @@ function recursiveDecent(ref: any){
                     lastPositionInTemplate[lastPositionInTemplateKey] = functionOutput;
                 }
             }
-        }else if(key != 'Attributes' && typeof ref[key] == "object"){
+        }else if(key != 'Attributes' && ref[key] instanceof Object){
             placeInTemplate.push(key);
             lastPositionInTemplate = ref;
             lastPositionInTemplateKey = key;
@@ -1418,12 +1418,12 @@ function verificationFunction(f: (o: any) => boolean, message: string): Verifica
 }
 
 export const isList = verificationFunction(
-    (o: any) => (typeof o === 'object' && o.constructor === Array),
+    (o: any) => (o instanceof Object && o.constructor === Array),
     'Expecting a list'
 );
 
 export const isObject = verificationFunction(
-    (o: any) => (typeof o === 'object' && o.constructor === Object),
+    (o: any) => (o instanceof Object && o.constructor === Object),
     'Expecting an object'
 );
 

testData/invalid/yaml/null_value.yaml

@@ -0,0 +1,5 @@
+Resources:
+  MyBucket:
+    Type: 'AWS::S3::Bucket'
+    Properties:
+      Tags: null