Raise a proper error message when an illegal value is used for a discrete attribute.
Raise a proper error message when an illegal value is used for a discrete attribute.

xflows/textflows,xflows/clowdflows,xflows/textflows,xflows/clowdflows-backend,Alshak/clowdflows,xflows/textflows,xflows/clowdflows,Alshak/clowdflows,xflows/textflows,xflows/clowdflows,xflows/clowdflows-backend,xflows/clowdflows,xflows/clowdflows-backend,Alshak/clowdflows,xflows/clowdflows-backend,xflows/textflows,Alshak/clowdflows,Alshak/clowdflows,Alshak/clowdflows,xflows/clowdflows,Alshak/clowdflows