def validate_optional_str_fields(self, messages):
FIELDS = [<EOL>'<STR_LIT>',<EOL>'<STR_LIT:version>',<EOL>'<STR_LIT>',<EOL>'<STR_LIT>',<EOL>'<STR_LIT>',<EOL>'<STR_LIT:description>'<EOL>]<EOL>messages = self.validate_str_fields(FIELDS, True, messages)<EOL>return messages<EOL>
Fields marked as optional and of type string in class
        docstring must be of a type that provides __str__ method.