DATAMONGO-884 - Avoid NPE when calling overridden Object method.

Prepare issue branch.
DATAMONGO-884 - Avoid NPE when calling overridden Object method.

We now initialise the proxy in case an Object-method is called that is overridden in the traget class.

Based on initial pull request: #152 of @juhgiyo.
Added additional test cases.

Original pull request: #153.