query_engine = self.index.as_query_engine(
            service_context=self.service_context,
            text_qa_template=qa_template_copy, 
            refine_template=refine_template_prompt,
            streaming=streaming,
            similarity_top_k=3, 
            doc_ids=doc_ids,
            verbose=True,
        )

'Response' object has no attribute 'response_gen'