Fixed nullable types issues

Fixed issues in Invalid handling of empty strings in tables when
converting to nullable enum types
Revert "Fixed nullable types issues"

This reverts commit 014320d2251431bfb6849897de9e41d7c0de452a.
Fixed nullable types issues
Updated changelog to contain nullable enum fix
Merge in master, resolve conflict in changelog.
Merge pull request #368 from techtalk/nullable_enum_fix

Nullable enum fix