Repository: langchain
Issue: REGRESSION: ChatLiteLLM: ValidationError only when using cache
Labels: 🤖:bug,🔌: openai

### 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 os
from pathlib import Path

from langchain.globals import set_verbose, set_debug, set_llm_cache
from langchain_community.chat_models import ChatLiteLLM
from langchain_community.cache import SQLiteCache
from langchain_core.output_parsers.string import StrOutputParser

os.environ["OPENAI_API_KEY"] = Path("OPENAI_API_KEY.txt").read_text().strip()
set_verbose(True)
set_debug(True)
Path("test_cache.db").unlink(missing_ok=True)
set_llm_cache(SQLiteCache(database_path="test_cache.db"))

llm = ChatLiteLLM(
    model_name="openai/gpt-4o",
    cache=True,
    verbose=True,
    temperature=0,
    )
print(llm.predict("this is a test"))  # works fine because cache empty
print("Success 1/2")
print(llm.predict("this is a test"))  # fails
print("Success 2/2")
```

### Error Message and Stack Trace (if applicable)
```
Success 1/2
[llm/start] [llm:ChatLiteLLM] Entering LLM run with input:
{
  "prompts": [
    "Human: this is a test"
  ]
}
Retrieving a cache value that could not be deserialized properly. This is likely due to the cache being in an older format. Please recreate your cache to avoid this error.
[llm/error] [llm:ChatLiteLLM] [3ms] LLM run errored with error:
"ValidationError(model='ChatResult', errors=[{'loc': ('generations', 0, 'type'), 'msg': \"unexpected value; permitted: 'ChatGeneration'\", 'type': 'value_error.const', 'ctx': {'given': 'Generation', 'permitted': ('ChatGeneration',)}}, {'loc': ('generations', 0, 'message'), 'msg': 'field required', 'type': 'value_error.missing'}, {'loc': ('generations', 0, '__root__'), 'msg': 'Error while initializing ChatGeneration', 'type': 'value_error'}])Traceback (most recent call last):\n\n\n  File \"/home/USER/.pyenv/versions/doctoolsllm/lib/python3.11/site-packages/langchain_core/language_models/chat_models.py\", line 446, in generate\n    self._generate_with_cache(\n\n\n  File \"/home/USER/.pyenv/versions/doctoolsllm/lib/python3.11/site-packages/langchain_core/language_models/chat_models.py\", line 634, in _generate_with_cache\n    return ChatResult(generations=cache_val)\n           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n\n\n  File \"/home/USER/.pyenv/versions/doctoolsllm/lib/python3.11/site-packages/pydantic/v1/main.py\", line 341, in __init__\n    raise validation_error\n\n\npydantic.v1.error_wrappers.ValidationError: 3 validation errors for ChatResult\ngenerations -> 0 -> type\n  unexpected value; permitted: 'ChatGeneration' (type=value_error.const; given=Generation; permitted=('ChatGeneration',))\ngenerations -> 0 -> message\n  field required (type=value_error.missing)\ngenerations -> 0 -> __root__\n  Error while initializing ChatGeneration (type=value_error)"
Traceback (most recent call last):
  File "/home/LOCAL_PATH/DocToolsLLM/test.py", line 23, in <module>
    print(llm.predict("this is a test"))
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/USER/.pyenv/versions/doctoolsllm/lib/python3.11/site-packages/langchain_core/_api/deprecation.py", line 148, in warning_emitting_wrapper
    return wrapped(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/USER/.pyenv/versions/doctoolsllm/lib/python3.11/site-packages/langchain_core/language_models/chat_models.py", line 885, in predict
    result = self([HumanMessage(content=text)], stop=_stop, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/USER/.pyenv/versions/doctoolsllm/lib/python3.11/site-packages/langchain_core/_api/deprecation.py", line 148, in warning_emitting_wrapper
    return wrapped(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/USER/.pyenv/versions/doctoolsllm/lib/python3.11/site-packages/langchain_core/language_models/chat_models.py", line 847, in __call__
    generation = self.generate(
                 ^^^^^^^^^^^^^^
  File "/home/USER/.pyenv/versions/doctoolsllm/lib/python3.11/site-packages/langchain_core/language_models/chat_models.py", line 456, in generate
    raise e
  File "/home/USER/.pyenv/versions/doctoolsllm/lib/python3.11/site-packages/langchain_core/language_models/chat_models.py", line 446, in generate
    self._generate_with_cache(
  File "/home/USER/.pyenv/versions/doctoolsllm/lib/python3.11/site-packages/langchain_core/language_models/chat_models.py", line 634, in _generate_with_cache
    return ChatResult(generations=cache_val)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/USER/.pyenv/versions/doctoolsllm/lib/python3.11/site-packages/pydantic/v1/main.py", line 341, in __init__
    raise validation_error
pydantic.v1.error_wrappers.ValidationError: 3 validation errors for ChatResult
generations -> 0 -> type
  unexpected value; permitted: 'ChatGeneration' (type=value_error.const; given=Generation; permitted=('ChatGeneration',))
generations -> 0 -> message
  field required (type=value_error.missing)
generations -> 0 -> __root__
  Error while initializing ChatGeneration (type=value_error)
```

### Description

* I want to use the caching with chatlitellm
* It started happening when I upgraded from version 1 of langchain. I confirm it happens in langchain 0.2.0 and 0.2.1

### System Info

System Information
------------------
> OS:  Linux
> OS Version:  #35~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Tue May  7 09:00:52 UTC 2
> Python Version:  3.11.7 (main, Dec 28 2023, 19:03:16) [GCC 11.4.0]

Package Information
-------------------
> langchain_core: 0.2.3
> langchain: 0.2.1
> langchain_community: 0.2.1
> langsmith: 0.1.67
> langchain_mistralai: 0.1.7
> langchain_openai: 0.1.8
> langchain_text_splitters: 0.2.0

Packages not installed (Not Necessarily a Problem)
--------------------------------------------------
The following packages were not found:

> langgraph
> langserve


litellm==1.39.6