我有一个使用创建的现有索引GPTVectorStoreIndex。但是，当我尝试使用该insert方法将新文档添加到现有索引时，出现以下错误：
AttributeError: 'list' object has no attribute 'get_text'
我更新索引的代码如下：
max_input_size = 4096
num_outputs = 5000
max_chunk_overlap = 256
chunk_size_limit = 3900
prompt_helper = PromptHelper(max_input_size, num_outputs, max_chunk_overlap, chunk_size_limit=chunk_size_limit)
llm_predictor = LLMPredictor(llm=OpenAI(temperature=0, model_name="gpt-3.5-turbo", max_tokens=num_outputs))
service_context = ServiceContext.from_defaults(llm_predictor=llm_predictor, prompt_helper=prompt_helper)
directory_path = "./trial_docs"
file_metadata = lambda x : {"filename": x}
reader = SimpleDirectoryReader(directory_path, file_metadata=file_metadata)
documents = reader.load_data()
print(type(documents))
index.insert(document = documents, service_context = service_context)