Validate hashed string

I have a field in an entity, password, which is held as a hashed string. I would like to check that it has a value but I am unable to pass it to a microflow to do this.  The field name does not appear in the list of attributes when creating an expression. How can I validate this field. 
1 answers

A bit late, but after having the same issue:

MendixHashString pwHash = (MendixHashString) __imendixobject.getMember(getContext(), pwMemberName);
pwHash.verifyValue(getContext(), password);