Fix NullPointerException Extracting Class symbols (#7934)

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/ASMHelper.java

@@ -5,6 +5,7 @@
 import static org.objectweb.asm.Type.getObjectType;
 
 import com.datadog.debugger.agent.Generated;
+import datadog.trace.util.Strings;
 import java.lang.reflect.Field;
 import java.lang.reflect.Modifier;
 import java.util.ArrayList;
@@ -17,6 +18,7 @@
 import org.objectweb.asm.signature.SignatureReader;
 import org.objectweb.asm.signature.SignatureVisitor;
 import org.objectweb.asm.tree.AbstractInsnNode;
+import org.objectweb.asm.tree.ClassNode;
 import org.objectweb.asm.tree.FieldInsnNode;
 import org.objectweb.asm.tree.FieldNode;
 import org.objectweb.asm.tree.InsnList;
@@ -331,6 +333,13 @@ private static int widenIntType(int sort) {
     return sort;
   }
 
+  public static String extractSuperClass(ClassNode classNode) {
+    if (classNode.superName == null) {
+      return Object.class.getTypeName();
+    }
+    return Strings.getClassName(classNode.superName);
+  }
+
   /** Wraps ASM's {@link org.objectweb.asm.Type} with associated generic types */
   public static class Type {
     private final org.objectweb.asm.Type mainType;

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

@@ -1,5 +1,6 @@
 package com.datadog.debugger.instrumentation;
 
+import static com.datadog.debugger.instrumentation.ASMHelper.extractSuperClass;
 import static com.datadog.debugger.instrumentation.ASMHelper.getStatic;
 import static com.datadog.debugger.instrumentation.ASMHelper.invokeConstructor;
 import static com.datadog.debugger.instrumentation.ASMHelper.invokeStatic;
@@ -37,7 +38,6 @@
 import datadog.trace.bootstrap.debugger.MethodLocation;
 import datadog.trace.bootstrap.debugger.ProbeId;
 import datadog.trace.bootstrap.debugger.util.Redaction;
-import datadog.trace.util.Strings;
 import java.lang.reflect.Field;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -1161,7 +1161,7 @@ private static void addInheritedFields(
       Limits limits,
       List<FieldNode> results,
       int fieldCount) {
-    String superClassName = Strings.getClassName(classNode.superName);
+    String superClassName = extractSuperClass(classNode);
     while (!superClassName.equals(Object.class.getTypeName())) {
       Class<?> clazz;
       try {
@@ -1215,7 +1215,7 @@ private static void addInheritedStaticFields(
       Limits limits,
       List<FieldNode> results,
       int fieldCount) {
-    String superClassName = Strings.getClassName(classNode.superName);
+    String superClassName = extractSuperClass(classNode);
     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(ASMHelper.extractSuperClass(classNode))
               .build();
       Scope classScope =
           Scope.builder(ScopeType.CLASS, sourceFile, classStartLine, classEndLine)