Unhandled Exception missing connectors key

[nickila]

Description
If connectors key in directory_users in user-sync-config.yml is missing or misspelled, it throws an unhandled exception.

Steps to reproduce
Change or remove the connectors key in user-sync-config.yml and run the UST.

Expected behavior
A clean error message should tell you to fix the connectors key.
Screenshots
If applicable, add screenshots to help explain your problem.

Environment

• UST version:
• OS type and version:
• Any other relevant info: