fix(model): prevent NPE when GenerateOptions is null in ChatModelBase…

[hangweizhang]

….stream()

When HarnessAgent.streamEvents() is called without explicitly setting generateOptions, the options field remains null and gets passed down to ChatModelBase.stream() and eventually to doStream() implementations. OllamaChatModel.doStream() directly called options.getToolChoice() without a null-check, causing a NullPointerException:
Cannot invoke "GenerateOptions.getToolChoice()" because "options" is null

The non-streaming call() path was not affected because ReActAgent.buildGenerateOptions() already falls back to GenerateOptions.builder().build() when generateOptions is null.

Fix:

• ChatModelBase.stream(): replace null options with GenerateOptions.builder().build() before delegating to doStream(), ensuring all subclass implementations receive non-null options
• OllamaChatModel.doStream(): add defensive null-check as well, in case doStream is called through other code paths
• Add unit tests verifying null options are handled safely

Closes #1644

AgentScope-Java Version

[The version of AgentScope-Java you are working on, e.g. 1.0.12, check your pom.xml dependency version or run mvn dependency:tree | grep agentscope-parent:pom(only mac/linux)]

Description

[Please describe the background, purpose, changes made, and how to test this PR]

Checklist

Please check the following items before code is ready to be reviewed.

• Code has been formatted with mvn spotless:apply
• All tests are passing (mvn test)
• Javadoc comments are complete and follow project conventions
• Related documentation has been updated (e.g. links, examples, etc.)
• Code is ready for review

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...java/io/agentscope/core/model/OllamaChatModel.java	66.66%	0 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!

[hangweizhang]

@LearningGp fix for NPE #1667 please review thx

[AgentScopeJavaBot]

🤖 AI Review

This PR fixes a NullPointerException in the streaming path when GenerateOptions is null — specifically when HarnessAgent.streamEvents() is called without explicitly setting generate options. The fix is applied at two levels: (1) ChatModelBase.stream() replaces null with a default GenerateOptions instance before delegating to doStream() and the tracer, which is the correct abstraction level to centralize this guard; (2) OllamaChatModel.doStream() adds a defensive null-check as belt-and-suspenders for potential direct invocations. The included unit tests cover null, default-replacement, and passthrough scenarios using a clean StubModel. The changes are minimal, focused, and well-aligned with the project's existing patterns. Closes #1644.