[MCP] Handle Ollama's deviation from the OpenAI tool streaming spec

[hanouticelina]

python equivalent of huggingface/huggingface.js#1512.

Even though Ollama advertises an OpenAI-compatible streaming API, it sends a json payload in delta.tool_calls[*].function.arguments in the first chunk, not an empty string as in the OpenAI spec. when the second chunk arrives with the real payload, we try to do None += "", which obviously raises an Error. This PR should fix that.

[Copilot]

Pull Request Overview

This PR fixes an error when handling tool call argument concatenations for Ollama's streaming API by ensuring that a None value is replaced with an empty string before concatenation.

• Introduces a safety mechanism to handle None argument values in tool calls.
• Ensures subsequent JSON payload chunks are concatenated without errors.

[Copilot]

[nitpick] The check and assignment for function.arguments being None is repeated; consider refactoring this logic into a helper function to reduce duplication and improve maintainability.

Suggested change

	if final_tool_calls[idx].function.arguments is None:
	final_tool_calls[idx].function.arguments = ""
	continue
	# safety before concatenating text to .function.arguments
	if final_tool_calls[idx].function.arguments is None:
	final_tool_calls[idx].function.arguments = ""
	self._ensure_arguments_initialized(final_tool_calls[idx].function)
	continue
	# safety before concatenating text to .function.arguments
	self._ensure_arguments_initialized(final_tool_calls[idx].function)

[HuggingFaceDocBuilderDev]

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