langchain ValueError: One input key expected got ['input', 'chat_history_lines']

Question

Trying to combine multiple memory types with a langchain conversational chain.

import os

from langchain.chains import ConversationChain

from langchain.memory import (
    ConversationBufferMemory,
    CombinedMemory,
    ConversationSummaryMemory,
    ConversationEntityMemory
)

from langchain.memory.prompt import ENTITY_MEMORY_CONVERSATION_TEMPLATE
from pydantic import BaseModel
from typing import List, Dict, Any

from langchain.llms import OpenAI

llm = OpenAI(openai_api_key=os.getenv('OPENAI_API_KEY'))

entity_memory = ConversationEntityMemory(llm=llm)

conv_memory = ConversationBufferMemory(memory_key="chat_history_lines", input_key="input")

summary_memory = ConversationSummaryMemory(llm=OpenAI(), input_key="input")

# Combined
memory = CombinedMemory(memories=[
    conv_memory, 
    #summary_memory,
    entity_memory
])

_DEFAULT_TEMPLATE = """
You are a helpful assistant.

Known entities:
{entities}

History:
{history}

Current conversation:
{chat_history_lines}

User: {input}

You:"""

PROMPT = PromptTemplate(
    input_variables=['entities', 'chat_history_lines', 'history', 'input'],
    template=_DEFAULT_TEMPLATE,
)

conversation = ConversationChain(
    llm=llm, 
    verbose=True,
    #prompt=ENTITY_MEMORY_CONVERSATION_TEMPLATE,
    prompt=PROMPT,
    memory=memory
)

conversation.predict(input="Hi!")

ValueError: One input key expected got ['input', 'chat_history_lines']

What do I have to change in order to use multiple memories in a conversation chain? Or do I have to use something else than ConversationChain?

Villainy