Repository: langchain
Issue: Not using Tools in Langchain_Ollama causes: 'NoneType' object is not iterable
Labels: investigate

### 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

from langchain_ollama import ChatOllama

llm = ChatOllama(
    model="llama3.1",
    temperature=0,
    disable_streaming=True
)

messages = [
    (
        "system",
        "You are a helpful assistant that translates English to French. Translate the user sentence.",
    ),
    ("human", "I love programming."),
]
ai_msg = llm.invoke(messages)
print(ai_msg)

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

Traceback (most recent call last):
  File "/home/user1/Repo/ollama-cloud/use4.py", line 16, in <module>
    ai_msg = llm.invoke(messages)
  File "/home/user1/Repo/ollama-cloud/venv/lib/python3.10/site-packages/langchain_core/language_models/chat_models.py", line 286, in invoke
    self.generate_prompt(
  File "/home/user1/Repo/ollama-cloud/venv/lib/python3.10/site-packages/langchain_core/language_models/chat_models.py", line 786, in generate_prompt
    return self.generate(prompt_messages, stop=stop, callbacks=callbacks, **kwargs)
  File "/home/user1/Repo/ollama-cloud/venv/lib/python3.10/site-packages/langchain_core/language_models/chat_models.py", line 643, in generate
    raise e
  File "/home/user1/Repo/ollama-cloud/venv/lib/python3.10/site-packages/langchain_core/language_models/chat_models.py", line 633, in generate
    self._generate_with_cache(
  File "/home/user1/Repo/ollama-cloud/venv/lib/python3.10/site-packages/langchain_core/language_models/chat_models.py", line 851, in _generate_with_cache
    result = self._generate(
  File "/home/user1/Repo/ollama-cloud/venv/lib/python3.10/site-packages/langchain_ollama/chat_models.py", line 648, in _generate
    final_chunk = self._chat_stream_with_aggregation(
  File "/home/user1/Repo/ollama-cloud/venv/lib/python3.10/site-packages/langchain_ollama/chat_models.py", line 560, in _chat_stream_with_aggregation
    tool_calls=_get_tool_calls_from_response(stream_resp),
  File "/home/user1/Repo/ollama-cloud/venv/lib/python3.10/site-packages/langchain_ollama/chat_models.py", line 71, in _get_tool_calls_from_response
    for tc in response["message"]["tool_calls"]:
TypeError: 'NoneType' object is not iterable

### Description

Trying to simple get a chat response from ChatOllama.

### System Info

System Information
------------------
> OS:  Linux
> OS Version:  #49~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Wed Nov  6 17:42:15 UTC 2
> Python Version:  3.10.12 (main, Nov  6 2024, 20:22:13) [GCC 11.4.0]

Package Information
-------------------
> langchain_core: 0.3.20
> langchain: 0.3.7
> langchain_community: 0.3.7
> langsmith: 0.1.144
> langchain_ollama: 0.2.0
> langchain_text_splitters: 0.3.2

Optional packages not installed
-------------------------------
> langserve

Other Dependencies
------------------
> aiohttp: 3.11.7
> async-timeout: 4.0.3
> dataclasses-json: 0.6.7
> httpx: 0.27.2
> httpx-sse: 0.4.0
> jsonpatch: 1.33
> numpy: 1.26.4
> ollama: 0.4.0
> orjson: 3.10.11
> packaging: 24.2
> pydantic: 2.10.1
> pydantic-settings: 2.6.1
> PyYAML: 6.0.2
> requests: 2.32.3
> requests-toolbelt: 1.0.0
> SQLAlchemy: 2.0.35
> tenacity: 9.0.0
> typing-extensions: 4.12.2