fix crash when using create_xml_agent with parameterless function as …

[QunBB]

When using create_xml_agent or create_json_chat_agent to create a agent, and the function corresponding to the tool is a parameterless function, the XMLAgentOutputParser or JSONAgentOutputParser will parse the tool input into an empty string, BaseTool will parse it into a positional argument.
So, the program will crash finally because we invoke a parameterless function but with a positional argument.Specially, below code will raise StopIteration in _parse_input

from langchain import hub
from langchain.agents import AgentExecutor, create_json_chat_agent, create_xml_agent
from langchain_openai import ChatOpenAI

prompt = hub.pull("hwchase17/react-chat-json")

llm = ChatOpenAI()

# agent = create_xml_agent(llm, tools, prompt)
agent = create_json_chat_agent(llm, tools, prompt)
agent_executor = AgentExecutor(agent=agent, tools=tools, verbose=True)

agent_executor.invoke(......)

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

1 Skipped Deployment

Name	Status	Preview	Comments	Updated (UTC)
langchain	⬜️ Ignored (Inspect)	Visit Preview		Dec 19, 2024 5:52pm

[QunBB]

@baskaryan I have added unit tests for the related pull request, please check it again.
The unit tests should raise StopIteration similarly with current code, as I mentioned above.So i think my code could be merged.

[efriis]

overall I think this looks good - as a heads up we're charging towards a 0.3 release right now, so core is in code freeze until that goes out

Will mark to review after 0.3 is out!