Handle edge cases in export

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

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

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

The issue does not name a file, test, or export entry point. Start by locating the export validation and error-handling path, then identify the edge cases covered by the issue and how current messages are produced. Done means the relevant validation failures provide more descriptive messages and the affected behavior is covered by tests.

Written by the indexing model from the issue text.