Description

Root Cause

The serializer and deserializer are inconsistent:

• A2AErrorTypeAdapter.write() emits "error": null for null errors
• parseResponseBody() assumes the key's presence implies a non-null object

The correct long-term fix is to also stop emitting "error": null in
A2AErrorTypeAdapter.write(), but this client-side guard is sufficient to
prevent the crash.

Impact

Without this fix, every non-streaming A2A call fails with ClassCastException
regardless of whether the response is actually an error.

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