DB-Import for nested elements fails due to missing default-value of parentid.

[datamints]

When creating a content-element with nested elements, parentid is configured as int in the database but in the TCA, no default value is configured (-> so it is handled as string).
In our case, this causes empty Strings to be passed in the INSERT-Query, which in turn caused an SQL-Error when trying to import.
We patched it locally by just adding 'default' => 0 in the TCA for parentid.