Update pipeline.py

pipeline.py

@@ -27,6 +27,7 @@ from langchain.chains import RetrievalQA, LLMChain
 from langchain.prompts import PromptTemplate
 from langchain.docstore.document import Document
 from langchain_core.caches import BaseCache
+from langchain_core.callbacks import CallbackManager
 # from langchain.callbacks.base import BaseCallbacks  # Updated import
 # from langchain.callbacks.manager import CallbackManager
 # from langchain.callbacks import StdOutCallbackHandler