Handle edge cases in export

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

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

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

Start by locating the export and store-handling entry points, then trace the existing error paths and reproduce the unspecified edge cases. Clarify which failures need more descriptive messages and define done as improved messages for the agreed cases, with coverage for those cases if the project has relevant tests.

Written by the indexing model from the issue text.