Fix NPE use cases when level name entities table is empty

[jloux-brapi]

Description

Story: BI-2818

Please include a summary of the change that was made.

Fixed a NPE that can happen when no level names are present in the DB for global level names, as well as a use case when the level name of a submitted OU with OU level program is submitted.

Dependencies

Testing

After merging this change verify that rerunning unit tests for BI-2803 works.

Checklist:

• I have performed a self-review of my own code
• I have tested my code and ensured it meets the acceptance criteria of the story
• I have commented my code, particularly in hard-to-understand areas
• I have either updated the source of truth or arranged for update with product owner if needed https://breedinginsight.atlassian.net/wiki/spaces/BI/pages/1559953409/Source+of+Truth