DeepSeekStreamFunctionCallingHelper#merge throw NoSuchElementException

[wallezhang]

Bug description
When calling DeepSeek using the stream approach and tools are invoked, the org.springframework.ai.deepseek.api.DeepSeekStreamFunctionCallingHelper#merge method returns a NoSuchElementException: null exception.

Analysis

An exception was thrown on line 98. The previous stream returned a tool call. The current stream returns an array of tool calls, which is an empty array rather than null. So the current.toolCalls().iterator().next() will throw an NoSuchElementException.

I think the judgement on line 94 should be current.toolCalls() != null && !current.toolCalls().isEmpty()

Environment
Spring AI version: 1.0.3
Java Version: 21
DeepSeek v3.1

Expected behavior
Return tools successfully. Don't throw exception.

[sunyuhan1998]

Thank you for your report. I've submitted a PR to fix this issue, and you can track the progress here: #4598