partners: (langchain-deepseek) fix deepseek-r1 always returns an empty reasoning_content when reasoning

[reatang]

Description

deepseek-r1 always returns an empty string reasoning_content to the first chunk when thinking, and sets reasoning_content to None when thinking is over, to determine when to switch to normal output.

Therefore, whether the reasoning_content field exists should be judged as None.

Demo

deepseek-r1 reasoning output:

{'delta': {'content': None, 'function_call': None, 'refusal': None, 'role': 'assistant', 'tool_calls': None, 'reasoning_content': ''}, 'finish_reason': None, 'index': 0, 'logprobs': None}
{'delta': {'content': None, 'function_call': None, 'refusal': None, 'role': None, 'tool_calls': None, 'reasoning_content': '好的'}, 'finish_reason': None, 'index': 0, 'logprobs': None}
{'delta': {'content': None, 'function_call': None, 'refusal': None, 'role': None, 'tool_calls': None, 'reasoning_content': '，'}, 'finish_reason': None, 'index': 0, 'logprobs': None}
{'delta': {'content': None, 'function_call': None, 'refusal': None, 'role': None, 'tool_calls': None, 'reasoning_content': '用户'}, 'finish_reason': None, 'index': 0, 'logprobs': None}
...

deepseek-r1 first normal output

...
{'delta': {'content': ' main', 'function_call': None, 'refusal': None, 'role': None, 'tool_calls': None, 'reasoning_content': None}, 'finish_reason': None, 'index': 0, 'logprobs': None}
{'delta': {'content': '\n\nimport', 'function_call': None, 'refusal': None, 'role': None, 'tool_calls': None, 'reasoning_content': None}, 'finish_reason': None, 'index': 0, 'logprobs': None}
...

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Name	Status	Preview	Comments	Updated (UTC)
langchain	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Apr 29, 2025 7:51am