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If any of the list shall be empty, set an disabled item stating that
nothing valid is found. This is better than the currently empty dialog.

Part of #239

If any of the menu shall be empty, set an disabled action stating that
nothing valid is found. This is better than the currently empty menu.

Part of #239

Samuel GAIST authored May 01, 2020 and Flavio TARSETTI committed May 01, 2020

Using isort this makes all files coherent