Fix case when field is not on request

asUnicode(REQUEST.get(fieldname)) returns the string "None" if
fieldname is not on request.

Don't test for stuff like None and '' if that is irrelevant, it's just
noise.
Convert more search parameters to their proper types
Merge branch 'github-main' into jean-fix-searchDocuments

Conflict (resolved):
	Products/CMFPlomino/PlominoForm.py
Merge pull request #387 from plomino/jean-fix-searchDocuments

Fix case when field is not on request