Different Error Message for Empty ZotCourse Import

[EricPedley]

If you use import from study list but don't paste anything, its error message mentions the Zotcourse import, but a different error message shows up if you actually import from Zotcourse, and it fails to mention the field being empty. If the error messages are different for each, they should be specific to what feature was trying to be used, and the Zotcourse error message should mention that the field was empty.

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