Guard Tomcat CoyoteAdapter advice against null-scope NPE

dd-java-agent/instrumentation/tomcat/tomcat-5.5/build.gradle

@@ -113,6 +113,7 @@ dependencies {
   testRuntimeOnly project(':dd-java-agent:instrumentation:websocket:jakarta-websocket-2.0')
 
   testImplementation testFixtures(project(':dd-java-agent:instrumentation:servlet:jakarta-servlet-5.0'))
+  testImplementation libs.bundles.junit5
 
   tomcat9TestImplementation group: 'org.apache.tomcat.embed', name: 'tomcat-embed-core', version: '9.+'
   tomcat9TestImplementation group: 'org.apache.tomcat.embed', name: 'tomcat-embed-websocket', version: '9.+'

dd-java-agent/instrumentation/tomcat/tomcat-5.5/src/main/java/datadog/trace/instrumentation/tomcat/TomcatServerInstrumentation.java

@@ -133,7 +133,12 @@ public static void extractParent(
 
     @Advice.OnMethodExit(onThrowable = Throwable.class, suppress = Throwable.class)
     public static void closeScope(@Advice.Local("parentScope") ContextScope scope) {
-      scope.close();
+      // scope can be null if extractParent() above threw before assigning it (the throwable is
+      // swallowed by suppress = Throwable.class), which would otherwise NPE here and mask the
+      // real failure.
+      if (scope != null) {
+        scope.close();
+      }
     }
   }
 
@@ -167,7 +172,12 @@ public static void onService(
 
     @Advice.OnMethodExit(onThrowable = Throwable.class, suppress = Throwable.class)
     public static void closeScope(@Advice.Local("serverScope") ContextScope serverScope) {
-      serverScope.close();
+      // serverScope can be null if onService() above threw before assigning it (the throwable is
+      // swallowed by suppress = Throwable.class), which would otherwise NPE here and mask the
+      // real failure.
+      if (serverScope != null) {
+        serverScope.close();
+      }
     }
 
     private void muzzleCheck(CoyoteAdapter adapter, Request request, Response response)

dd-java-agent/instrumentation/tomcat/tomcat-5.5/src/test/java/datadog/trace/instrumentation/tomcat/TomcatServerInstrumentationTest.java

@@ -0,0 +1,49 @@
+package datadog.trace.instrumentation.tomcat;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import datadog.context.Context;
+import datadog.context.ContextScope;
+import org.junit.jupiter.api.Test;
+
+class TomcatServerInstrumentationTest {
+
+  private static final class RecordingScope implements ContextScope {
+    private boolean closed;
+
+    @Override
+    public Context context() {
+      return null;
+    }
+
+    @Override
+    public void close() {
+      closed = true;
+    }
+  }
+
+  @Test
+  void contextTrackingAdviceCloseScopeToleratesNullScope() {
+    assertDoesNotThrow(() -> TomcatServerInstrumentation.ContextTrackingAdvice.closeScope(null));
+  }
+
+  @Test
+  void contextTrackingAdviceCloseScopeClosesNonNullScope() {
+    RecordingScope scope = new RecordingScope();
+    TomcatServerInstrumentation.ContextTrackingAdvice.closeScope(scope);
+    assertTrue(scope.closed);
+  }
+
+  @Test
+  void serviceAdviceCloseScopeToleratesNullScope() {
+    assertDoesNotThrow(() -> TomcatServerInstrumentation.ServiceAdvice.closeScope(null));
+  }
+
+  @Test
+  void serviceAdviceCloseScopeClosesNonNullScope() {
+    RecordingScope scope = new RecordingScope();
+    TomcatServerInstrumentation.ServiceAdvice.closeScope(scope);
+    assertTrue(scope.closed);
+  }
+}