feat: allow runAsync with null newMessage

[wenhaozhao]

feat: allow runAsync with null newMessage

[gemini-code-assist]

Summary of Changes

Hello @wenhaozhao, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a feature that allows the runAsync method to accept null values for its newMessage parameter. This enhancement provides greater flexibility for callers of the runAsync method, enabling scenarios where a message might not always be present.

Highlights

• runAsync method modification to accept null newMessage: The runAsync method in core/src/main/java/com/google/adk/runner/Runner.java has been updated to use Optional.ofNullable(newMessage) instead of Optional.of(newMessage). This change allows the newMessage parameter to be null when invoking the newInvocationContext method, providing more flexibility for callers.

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[gemini-code-assist]

Code Review

This pull request correctly modifies the runAsync method to handle a null newMessage by using Optional.ofNullable. This is a good change that increases the flexibility of the method. My review includes one suggestion to improve code clarity and maintainability by explicitly annotating the newMessage parameter as @Nullable in the relevant method signatures.

[Poggecci]

Thank you for your contribution!

Ooc, what is your usecase for allowing new message to be null?

[wenhaozhao]

Thank you for your contribution!

Ooc, what is your usecase for allowing new message to be null?

In my project, I need to restore memory content from persistent storage into the session so that the agent can continue execution without the user needing to input a new prompt.

Additionally, this operation was allowed in version 0.2.0, but an incompatibility arose after upgrading to 0.2.1-snapshot.

[Jacksunwei]

@wenhaozhao This is actually not a valid input. The recommended approach is to add a meanful User content to continue the conversation.

For context, in ADK python, we're introducing "resume" to allow the Runner to resume from a previous incomplete state, but that's also different from taking a null new_message.

[wenhaozhao]

@wenhaozhao This is actually not a valid input. The recommended approach is to add a meanful User content to continue the conversation.

For context, in ADK python, we're introducing "resume" to allow the Runner to resume from a previous incomplete state, but that's also different from taking a null new_message.

From a logical effect perspective, "resume" is indeed different from a "null-message." However, from a practical effect standpoint, it's similar to: restoring the history to the session, and then by submitting a null-message, causing the runner to resume execution from its previous state.

Currently, adk-java does not have an entry point (or equivalent functionality) similar to "resume." Additionally, "resume" is indeed a better idea.