fix: Create a new session resumption config if it's None

Co-authored-by: Xiang (Sean) Zhou <seanzhougoogle@google.com>
PiperOrigin-RevId: 853933839

Author: seanzhougoogle

src/google/adk/flows/llm_flows/base_llm_flow.py

@@ -116,6 +116,10 @@ async def run_live(
           attempt += 1
           if not llm_request.live_connect_config:
             llm_request.live_connect_config = types.LiveConnectConfig()
+          if not llm_request.live_connect_config.session_resumption:
+            llm_request.live_connect_config.session_resumption = (
+                types.SessionResumptionConfig()
+            )
           llm_request.live_connect_config.session_resumption.handle = (
               invocation_context.live_session_resumption_handle
           )