Make definition column on object type table non nullable

[kkajla12]

Is your feature request related to a problem? Please describe.
As currently defined, object type records in the database are allowed to have a NULL definition (this is also currently the default value if no value is provided for that column as part of the insert).

Describe the solution you'd like
The above behavior is incorrect and we should enforce that the definition column is not nullable at the database level (in addition to the application level enforcement already in place).

Describe alternatives you've considered
N/A

Additional context
We'll need to make sure this behavior is updated for all supported databases. Any migrations added to enforce this non-nullable constraint on the definition column should also be sure to handle existing object type records that might have a NULL definition.