Update app.py

app.py

@@ -10,8 +10,8 @@ from langchain.text_splitter import RecursiveCharacterTextSplitter
 from langchain.vectorstores import FAISS
 from langchain_community.embeddings import HuggingFaceEmbeddings
 from langchain_community.chat_models import ChatOpenAI
-from langchain.prompts import ChatPromptTemplate
-from langchain_core.messages import HumanMessage, AIMessage, SystemMessage, MessagesPlaceholder
+from langchain.prompts import ChatPromptTemplate, MessagesPlaceholder  # MessagesPlaceholder from here
+from langchain_core.messages import HumanMessage, AIMessage, SystemMessage  # Remove MessagesPlaceholder from here
 from langchain.chains import ConversationalRetrievalChain
 from langchain_core.runnables import RunnablePassthrough
 from langchain.memory import ConversationBufferMemory