def METHOD_NAME(self, flow: HTTPFlow):
    """Checks if the response should be included in the URL based on the index_filter and adds it to the URL index
    if appropriate.
    """
    if isinstance(self.index_filter, str) or self.index_filter is None:
        raise ValueError("Invalid filter expression.")
    else:
        if self.index_filter(flow):
            self.writer.add_url(flow)