What

When exporting subdomain data, if the database table does not exist for a given domain, database.export_data() returns None. The subsequent call to rows.dataset and rows.export() raises AttributeError: 'NoneType' object has no attribute 'scalar' (or similar).

Also, the current code does not gracefully handle missing tables, leading to thread-related SQLite errors when the database is accessed from multiple threads.

Fix

• Added a null check for rows in export_data() and do_export(). If rows is None, log an error and return early to avoid the attribute error.
• This prevents the crash and allows the exporter to continue processing other domains.

Closes #389