If the check for canImport() throws an exception, the error is not caught and surfaced in a meaningful way.
To resolve this, move the start of the 'try' so that it includes the call of canImport()
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I have issues importing a CM document, but the error is indeed unhelpful by being empty.
When I found this issue I thought it cold help, but in ContentModelDocumentationCommands class, the try{} includes the canImport() call.