If there is data, parse it, otherwise return None.

def _get_input_data(self, request):
        """ If there is data, parse it, otherwise return None. """
        # only PUT and POST should provide data
        if not self._is_data_method(request):
            return None

        content = [row for row in request.read()]
        content = ''.join(content) if content else None
        return self._parse_input_data(content, request) if content else None