Repository: langchain
Issue: Given example fails
Labels: Ɑ:  core

### Checked other resources

- [X] I added a very descriptive title to this issue.
- [X] I searched the LangChain documentation with the integrated search.
- [X] I used the GitHub search to find a similar question and didn't find it.
- [X] I am sure that this is a bug in LangChain rather than my code.
- [X] The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package).

### Example Code

```python
import pandas as pd
from langchain_openai import ChatOpenAI
from langchain_core.output_parsers import JsonOutputParser
from langchain_experimental.agents.agent_toolkits import create_pandas_dataframe_agent

# Step 1: Load your DataFrame
df = pd.read_csv("https://raw.githubusercontent.com/pandas-dev/pandas/main/doc/data/titanic.csv")

# Step 2: Initialize the LLM
model = ChatOpenAI(temperature=0)

# Step 3: Define the JsonOutputParser
parser = JsonOutputParser()

# Step 4: Create a Pandas DataFrame Agent
agent = create_pandas_dataframe_agent(model, df, verbose=True)

# Step 5: Chain the components
chain = agent | parser

# Step 6: Invoke the chain with a query
result = chain.invoke({"query": "How many people survived?"})

# Output the result
print(result)
```

### Error Message and Stack Trace (if applicable)

new AgentExecutor chain...
Thought: To find out how many people survived, I need to sum the 'Survived' column in the dataframe.
Action: python_repl_ast
Action Input: df['Survived'].sum()342I now know the final answer
Final Answer: 342 people survived.

> Finished chain.
Traceback (most recent call last):
  File "/Users/joseph/Projects/chat_bot/scratch.py", line 29, in <module>
    result = chain.invoke("How many people survived?")
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/joseph/Projects/chat_bot/.venv/lib/python3.12/site-packages/langchain_core/runnables/base.py", line 3024, in invoke
    input = context.run(step.invoke, input, config)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/joseph/Projects/chat_bot/.venv/lib/python3.12/site-packages/langchain_core/output_parsers/base.py", line 202, in invoke
    return self._call_with_config(
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/joseph/Projects/chat_bot/.venv/lib/python3.12/site-packages/langchain_core/runnables/base.py", line 1927, in _call_with_config
    context.run(
  File "/Users/joseph/Projects/chat_bot/.venv/lib/python3.12/site-packages/langchain_core/runnables/config.py", line 396, in call_func_with_variable_args
    return func(input, **kwargs)  # type: ignore[call-arg]
           ^^^^^^^^^^^^^^^^^^^^^
  File "/Users/joseph/Projects/chat_bot/.venv/lib/python3.12/site-packages/langchain_core/output_parsers/base.py", line 203, in <lambda>
    lambda inner_input: self.parse_result([Generation(text=inner_input)]),
                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/joseph/Projects/chat_bot/.venv/lib/python3.12/site-packages/langchain_core/load/serializable.py", line 125, in __init__
    super().__init__(*args, **kwargs)
  File "/Users/joseph/Projects/chat_bot/.venv/lib/python3.12/site-packages/pydantic/main.py", line 212, in __init__
    validated_self = self.__pydantic_validator__.validate_python(data, self_instance=self)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
pydantic_core._pydantic_core.ValidationError: 1 validation error for Generation
text
  Input should be a valid string [type=string_type, input_value={'input': 'How many peopl... '342 people survived.'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.9/v/string_type

### Description

I was getting that failure in my code and went to the site and chatted with the input `how can I chain an Agent with a JsonOutputParser`

### System Info


System Information
------------------
> OS:  Darwin
> OS Version:  Darwin Kernel Version 24.1.0: Thu Oct 10 21:03:11 PDT 2024; root:xnu-11215.41.3~2/RELEASE_ARM64_T6020
> Python Version:  3.12.7 (main, Oct  8 2024, 17:22:48) [Clang 16.0.0 (clang-1600.0.26.3)]

Package Information
-------------------
> langchain_core: 0.3.15
> langchain: 0.3.7
> langchain_community: 0.3.4
> langsmith: 0.1.139
> langchain_experimental: 0.3.2
> langchain_huggingface: 0.1.2
> langchain_ollama: 0.2.0
> langchain_openai: 0.2.5
> langchain_text_splitters: 0.3.2

Optional packages not installed
-------------------------------
> langgraph
> langserve

Other Dependencies
------------------
> aiohttp: 3.10.10
> async-timeout: Installed. No version info available.
> dataclasses-json: 0.6.7
> httpx: 0.27.2
> httpx-sse: 0.4.0
> huggingface-hub: 0.26.2
> jsonpatch: 1.33
> numpy: 1.26.4
> ollama: 0.3.3
> openai: 1.53.0
> orjson: 3.10.10
> packaging: 24.1
> pydantic: 2.9.2
> pydantic-settings: 2.6.1
> PyYAML: 6.0.2
> requests: 2.32.3
> requests-toolbelt: 1.0.0
> sentence-transformers: 3.2.1
> SQLAlchemy: 2.0.36
> tenacity: 9.0.0
> tiktoken: 0.8.0
> tokenizers: 0.20.1
> transformers: 4.46.1
> typing-extensions: 4.12.2