Return optional Annotation Properties (0 or greater).

def _get_properties(self, fldstr):
        """Return optional Annotation Properties (0 or greater)."""
        prop2val = {}
        props = self._rd_fld_vals("Properties", fldstr, False)  # Get set
        go_evidence = None
        for prop in props:
            # There can be more properties than 'go_evidence',
            # but currently we see only 'go_evidence'.
            # Upon encountering updates, evaluate and update code to support ...
            if prop[:12] == 'go_evidence=':
                assert go_evidence is None, "MORE THAN ONE EVIDENCE CODE FOUND"
                go_evidence = prop[12:]
            else:
                assert False, "UNPROGRAMMED PROPERTY({P})".format(P=prop)
        ## TBD: Is 'go_evidence' still used? Replaced by ECO? And eco2group
        ## assert go_evidence is not None, "go_evidence == None"
        ## prop2val['go_evidence'] = go_evidence
        if go_evidence is not None:
            prop2val['go_evidence'] = go_evidence
        return prop2val