def parse_value(self, querydict):
value = self.field.get_value(querydict)<EOL>if value in (None, fields.empty, '<STR_LIT>'):<EOL><INDENT>return None<EOL><DEDENT>return self.field.to_internal_value(value)<EOL>
extract value

        extarct value from querydict and convert it to native
        missing and empty values result to None