Update controllers documentation

**Problem**
When working with models, the error messages could be more descriptive.

**Suggestion**
Improve error handling and add detailed error messages.

**Context**
This would help with debugging and maintenance.

No file, entry point, or test is named. Start by locating the controllers and model error-handling paths, then clarify whether the intended outcome is documentation updates or changed error messages; done means the agreed scope is implemented and verified.

Written by the indexing model from the issue text.