Fix Ollama streaming null generate options

[SPUERSAIYAN]

AgentScope-Java Version

Version: agentscope-harness:2.0.0-RC1
Java: 21

Description

Fixes #1644
This PR fixes a NullPointerException in the Ollama streaming path when GenerateOptions is not explicitly configured.

Background:
HarnessAgent.streamEvents() can ultimately call the Ollama model streaming API with GenerateOptions == null. OllamaChatModel.doStream(...) previously accessed options.getToolChoice() directly, which caused an NPE. Non-streaming calls were unaffected because the options conversion path already handled null values.

Changes made:

• Added a null-safe default GenerateOptions.builder().build() in OllamaChatModel.doStream(...).
• Added a regression test covering OllamaChatModel.stream(..., null) to ensure streaming works without explicit generate options.

How to test:

• mvn -pl agentscope-core -Dtest=OllamaChatModelTest test
• mvn -pl agentscope-core -Dtest=OllamaChatModelTest#testStreamChatRequestWithNullOptions test
• git diff --check

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

[AgentScopeJavaBot]

🤖 AI Review

This PR fixes a NullPointerException in OllamaChatModel.doStream() when GenerateOptions is null. The base class ChatModelBase contract explicitly documents options as "null to use defaults", but doStream() called options.getToolChoice() without a null-guard, causing an NPE. The fix introduces a null-safe effectiveOptions fallback (GenerateOptions.builder().build()) — a clean, minimal one-line guard that is consistent with the project's existing null-handling patterns (e.g., OllamaOptions.fromGenerateOptions(null) already returns a default instance, and the constructor null-guards defaultOptions). A well-structured regression test covers stream(messages, null, null). The non-streaming chat() path was already null-safe via OllamaOptions.fromGenerateOptions(). No issues found.