Bugfix: Convert - Correctly error if a valid mask has not been selected #587

Job	Run time
pip (ubuntu-latest, cpu)	1m 23s
conda (ubuntu-latest, nvidia)	6m 7s
pip (windows-latest, cpu)	3m 40s
conda (ubuntu-latest, cpu)	6m 9s
pip (windows-latest, directml)	5m 28s
conda (macos-latest, nvidia)	6s
conda (macos-latest, cpu)	7s
conda (windows-latest, nvidia)	6m 1s
conda (windows-latest, cpu)	6m 1s
conda (ubuntu-latest, rocm)	5m 57s
conda (windows-latest, directml)	6m 1s
	47m 0s

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