Migration script generate null value for a field without data and import script can't import these fields because a string type required  

Steps to reproduce

1. Create a Content_type without setting a description and set identifier to test

2. Create a migration file with php bin/console ibexa:migrations:generate --type=content_type --mode=create --match-property=content_type_identifier --value=test

3. Run php bin/console ibexa:migrations:migrate at the destination 

Result

Throws Exeption with: Argument '$contentTypeCreateStruct>descriptions['eng-GB']' is invalid: value must be of type 'string'

Expected Result:
The generated migration file should be correct and importable