Fix exception message handling to prevent empty message field

Co-authored-by: trask <[email protected]>

Author: Copilot

agent/agent-tooling/src/main/java/com/microsoft/applicationinsights/agent/internal/classicsdk/TelemetryUtil.java

@@ -61,6 +61,12 @@ private static ExceptionDetailBuilder createWithStackInfo(
     if (Strings.isNullOrEmpty(exceptionMessage)) {
       exceptionMessage = exception.getClass().getName();
     }
+    
+    // Defensive check to ensure the message is never null or empty
+    if (Strings.isNullOrEmpty(exceptionMessage)) {
+      exceptionMessage = "Unknown Exception";
+    }
+    
     exceptionDetails.setMessage(exceptionMessage);
 
     if (parentExceptionDetails != null) {

agent/agent-tooling/src/test/java/com/microsoft/applicationinsights/agent/internal/classicsdk/ExceptionMessageBehaviorTest.java

@@ -0,0 +1,83 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+package com.microsoft.applicationinsights.agent.internal.classicsdk;
+
+import com.azure.monitor.opentelemetry.autoconfigure.implementation.utils.Strings;
+import org.junit.jupiter.api.Test;
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class ExceptionMessageBehaviorTest {
+
+  @Test
+  public void testNullPointerExceptionMessageBehavior() {
+    // Test the exact scenario from the problem statement
+    NullPointerException exception = new NullPointerException();
+    
+    // Check the message
+    String message = exception.getMessage();
+    assertThat(message).isNull();
+    
+    // Apply the TelemetryUtil logic
+    String exceptionMessage = message;
+    if (Strings.isNullOrEmpty(exceptionMessage)) {
+      exceptionMessage = exception.getClass().getName();
+    }
+    
+    // The final message should be the class name
+    assertThat(exceptionMessage).isEqualTo("java.lang.NullPointerException");
+    assertThat(exceptionMessage).isNotEmpty();
+    assertThat(exceptionMessage).isNotNull();
+  }
+
+  @Test
+  public void testNullPointerExceptionWithEmptyMessage() {
+    // Test the scenario with empty string
+    NullPointerException exception = new NullPointerException("");
+    
+    // Check the message
+    String message = exception.getMessage();
+    assertThat(message).isEqualTo("");
+    
+    // Apply the TelemetryUtil logic
+    String exceptionMessage = message;
+    if (Strings.isNullOrEmpty(exceptionMessage)) {
+      exceptionMessage = exception.getClass().getName();
+    }
+    
+    // The final message should be the class name
+    assertThat(exceptionMessage).isEqualTo("java.lang.NullPointerException");
+    assertThat(exceptionMessage).isNotEmpty();
+    assertThat(exceptionMessage).isNotNull();
+  }
+
+  @Test
+  public void testRuntimeExceptionMessageBehavior() {
+    // Test with RuntimeException
+    RuntimeException exception = new RuntimeException();
+    
+    // Check the message
+    String message = exception.getMessage();
+    assertThat(message).isNull();
+    
+    // Apply the TelemetryUtil logic
+    String exceptionMessage = message;
+    if (Strings.isNullOrEmpty(exceptionMessage)) {
+      exceptionMessage = exception.getClass().getName();
+    }
+    
+    // The final message should be the class name
+    assertThat(exceptionMessage).isEqualTo("java.lang.RuntimeException");
+    assertThat(exceptionMessage).isNotEmpty();
+    assertThat(exceptionMessage).isNotNull();
+  }
+
+  @Test
+  public void testStringIsNullOrEmptyBehavior() {
+    // Test the Strings.isNullOrEmpty behavior with various inputs
+    assertThat(Strings.isNullOrEmpty(null)).isTrue();
+    assertThat(Strings.isNullOrEmpty("")).isTrue();
+    assertThat(Strings.isNullOrEmpty("   ")).isFalse(); // Whitespace is not empty
+    assertThat(Strings.isNullOrEmpty("test")).isFalse();
+  }
+}

agent/agent-tooling/src/test/java/com/microsoft/applicationinsights/agent/internal/classicsdk/ExceptionTelemetryBuilderTest.java

@@ -57,12 +57,17 @@ public void testExceptionMessageHandling() {
       String testMessage = testMessages[i];
       String expectedResult = expectedResults[i];
 
-      // Simulate TelemetryUtil logic
+      // Simulate TelemetryUtil logic with defensive check
       String exceptionMessage = testMessage;
       if (Strings.isNullOrEmpty(exceptionMessage)) {
         exceptionMessage = "java.lang.NullPointerException";
       }
 
+      // Defensive check to ensure the message is never null or empty
+      if (Strings.isNullOrEmpty(exceptionMessage)) {
+        exceptionMessage = "Unknown Exception";
+      }
+      
       assertThat(exceptionMessage).isEqualTo(expectedResult);
     }
   }