PLAT-4609 - Oracle DB - Handle empty string

Encode and decode empty string to avoid Oracle mapping to null. Add a single space to empty string and all strings that are only spaces.

Essentially, this is a relatively simple mapping to workaround the Oracle empty string is null issue. Dedicated Spring templates do the work and hide it from application logic. As far as I can tell, this covers most uses of the API, but it would be no surprise to find edge cases in the future.

May be worth adding a comment or code to indicate that this is implicitly testing empty String berhaviour. Alternatively, raise a separate JIRA?