Add "no value" and "unknown value" as possible values for a Wikidata statement

Is your feature request related to a problem or area of OpenRefine? Please describe. It would be great if there could be a possibility to put "no value" or "unknown value" as a value for statements in a Wikidata scheme.

Describe the solution you'd like When editing the Wikidata scheme for exporting values, it would be nice to have an additional command to add a "no value" or "unknown value" option, much like the Wikidata one (see image below).

Describe alternatives you've considered none

Additional context none