Fix NullPointerException Extracting Class symbols

In rare cases, class super name is null (normally only for
java.lag.Object). Handle nicely this case.

Author: jpbempel

dd-java-agent/agent-debugger/src/main/java/com/datadog/debugger/instrumentation/CapturedContextInstrumentor.java

@@ -1161,7 +1161,10 @@ private static void addInheritedFields(
       Limits limits,
       List<FieldNode> results,
       int fieldCount) {
-    String superClassName = Strings.getClassName(classNode.superName);
+    String superClassName =
+        classNode.superName != null
+            ? Strings.getClassName(classNode.superName)
+            : Object.class.getTypeName();
     while (!superClassName.equals(Object.class.getTypeName())) {
       Class<?> clazz;
       try {
@@ -1215,7 +1218,10 @@ private static void addInheritedStaticFields(
       Limits limits,
       List<FieldNode> results,
       int fieldCount) {
-    String superClassName = Strings.getClassName(classNode.superName);
+    String superClassName =
+        classNode.superName != null
+            ? Strings.getClassName(classNode.superName)
+            : Object.class.getTypeName();
     while (!superClassName.equals(Object.class.getTypeName())) {
       Class<?> clazz;
       try {

dd-java-agent/agent-debugger/src/main/java/com/datadog/debugger/symbol/SymbolExtractor.java

@@ -51,7 +51,7 @@ private static Scope extractScopes(ClassNode classNode, String jarName) {
               .addModifiers(extractClassModifiers(classNode.access))
               .addInterfaces(extractInterfaces(classNode))
               .addAnnotations(extractAnnotations(classNode.visibleAnnotations))
-              .superClass(Strings.getClassName(classNode.superName))
+              .superClass(extractSuperClass(classNode))
               .build();
       Scope classScope =
           Scope.builder(ScopeType.CLASS, sourceFile, classStartLine, classEndLine)
@@ -72,6 +72,13 @@ private static Scope extractScopes(ClassNode classNode, String jarName) {
     }
   }
 
+  private static String extractSuperClass(ClassNode classNode) {
+    if (classNode.superName == null) {
+      return Object.class.getTypeName();
+    }
+    return Strings.getClassName(classNode.superName);
+  }
+
   private static Collection<String> extractInterfaces(ClassNode classNode) {
     if (classNode.interfaces.isEmpty()) {
       return Collections.emptyList();