Merge https://github.com/google/adk-python/pull/3280 Fixes: #3281 COPYBARA_INTEGRATE_REVIEW=https://github.com/google/adk-python/pull/3280 from MarlzRana:marlzrana/fix-nullable-types-w-gen-ai-bump ad28b82cbdbb7980406086787e098bbe6478a354 PiperOrigin-RevId: 824659954