fix: Safely handle empty model in GoogleSearchTool request processor

Author: hemasekhar-p

core/src/main/java/com/google/adk/tools/GoogleSearchTool.java

@@ -61,7 +61,7 @@ public Completable processLlmRequest(
     ImmutableList.Builder<Tool> updatedToolsBuilder = ImmutableList.builder();
     updatedToolsBuilder.addAll(existingTools);
 
-    String model = llmRequestBuilder.build().model().get();
+    String model = llmRequestBuilder.build().model().orElse(null);
     if (model != null && (model.startsWith("gemini-2") || model.startsWith("gemini-3"))) {
 
       updatedToolsBuilder.add(Tool.builder().googleSearch(GoogleSearch.builder().build()).build());

core/src/test/java/com/google/adk/tools/BaseToolTest.java

@@ -356,6 +356,16 @@ public void runAsync_withClassAndObjectMapper_convertsArguments() throws Excepti
     testObserver.assertValue(expected);
   }
 
+  @Test
+  public void testProcessLlmRequest_WithNoModel_DoesNotThrowsException() {
+    GoogleSearchTool tool = GoogleSearchTool.INSTANCE;
+    LlmRequest.Builder requestBuilder = LlmRequest.builder();
+
+    tool.processLlmRequest(requestBuilder, null);
+
+    assertNotNull(requestBuilder);
+  }
+
   public record TestToolArgs(int i, String s) {}
 
   @Test