Program: 42101
Project: 42101
Buggy source:
public static ItemWrench makeMeAWrench(){
  ArrayList<ClassNode> nodes=new ArrayList<>(ItemHelper.wrenchClassNames.length);
  ArrayList<String> ifaceList=new ArrayList<>(ItemHelper.wrenchClassNames.length);
  LinkedList<String> toCheck=Lists.newLinkedList();
  Collections.addAll(toCheck,ItemHelper.wrenchClassNames);
  while (!toCheck.isEmpty()) {
    try {
      String wrenchClassName=toCheck.poll();
      byte[] classBytes=loader.getClassBytes(wrenchClassName);
      if (classBytes != null) {
        ClassNode node=new ClassNode(ASM5);
        ClassReader reader=new ClassReader(classBytes);
        reader.accept(node,ClassReader.EXPAND_FRAMES);
        for (        String anInterface : node.interfaces) {
          toCheck.add(anInterface.replace('/','.'));
        }
        nodes.add(node);
        ifaceList.add(wrenchClassName.replace('.','/'));
      }
    }
 catch (    IOException ignore) {
    }
  }
  if (nodes.isEmpty())   return new ItemWrench();
  HashSet<String> methods=new HashSet<>();
  try {
    byte[] classBytes=loader.getClassBytes(ItemWrench.class.getName());
    ClassNode node=new ClassNode(ASM5);
    ClassReader reader=new ClassReader(classBytes);
    reader.accept(node,ClassReader.EXPAND_FRAMES);
    for (    MethodNode method : node.methods) {
      methods.add(getMethodDesc(method));
    }
  }
 catch (  IOException ignore) {
  }
  ClassWriter cw=new ClassWriter(0);
  MethodVisitor mv;
  String name="String_Node_Str";
  String superName=Type.getInternalName(ItemWrench.class);
  String[] ifaces=ifaceList.toArray(new String[ifaceList.size()]);
  cw.visit(V1_6,ACC_PUBLIC | ACC_SUPER,name,null,superName,ifaces);
  cw.visitSource("String_Node_Str",null);
{
    mv=cw.visitMethod(ACC_PUBLIC,"String_Node_Str","String_Node_Str",null,null);
    mv.visitCode();
    mv.visitVarInsn(ALOAD,0);
    mv.visitMethodInsn(INVOKESPECIAL,superName,"String_Node_Str","String_Node_Str",false);
    mv.visitInsn(RETURN);
    mv.visitMaxs(1,1);
    mv.visitEnd();
  }
  for (  ClassNode node : nodes) {
    for (    MethodNode method : node.methods) {
      String mn=getMethodDesc(method);
      if (methods.contains(mn))       continue;
      methods.add(mn);
      Type returnType=Type.getReturnType(method.desc);
      int returnOpCode=returnType.getOpcode(IRETURN);
      mv=cw.visitMethod(ACC_PUBLIC,method.name,method.desc,null,null);
      mv.visitCode();
switch (returnOpCode) {
case RETURN:
        break;
case IRETURN:
      mv.visitInsn(returnType == Type.BOOLEAN_TYPE ? ICONST_1 : ICONST_0);
    break;
case LRETURN:
  mv.visitInsn(LCONST_0);
break;
case FRETURN:
mv.visitInsn(FCONST_0);
break;
case DRETURN:
mv.visitInsn(DCONST_0);
break;
case ARETURN:
mv.visitInsn(ACONST_NULL);
break;
}
mv.visitInsn(returnOpCode);
mv.visitInsn(RETURN);
mv.visitMaxs(returnOpCode != RETURN ? 1 : 0,1 + Type.getArgumentTypes(method.desc).length);
mv.visitEnd();
}
}
cw.visitEnd();
Class<?> ret=(new ASMClassLoader()).define(name,cw.toByteArray());
try {
return (ItemWrench)ret.newInstance();
}
 catch (Throwable e) {
throw new RuntimeException(e);
}
}

Fixed version (ground truth):
public static ItemWrench makeMeAWrench(){
  ArrayList<ClassNode> nodes=new ArrayList<>(ItemHelper.wrenchClassNames.length);
  ArrayList<String> ifaceList=new ArrayList<>(ItemHelper.wrenchClassNames.length);
  LinkedList<String> toCheck=Lists.newLinkedList();
  Collections.addAll(toCheck,ItemHelper.wrenchClassNames);
  while (!toCheck.isEmpty()) {
    try {
      String wrenchClassName=toCheck.poll();
      byte[] classBytes=loader.getClassBytes(wrenchClassName);
      if (classBytes != null) {
        ClassNode node=new ClassNode(ASM5);
        ClassReader reader=new ClassReader(classBytes);
        reader.accept(node,ClassReader.EXPAND_FRAMES);
        for (        String anInterface : node.interfaces) {
          toCheck.add(anInterface.replace('/','.'));
        }
        nodes.add(node);
        ifaceList.add(wrenchClassName.replace('.','/'));
      }
    }
 catch (    IOException ignore) {
    }
  }
  if (nodes.isEmpty())   return new ItemWrench();
  HashSet<String> methods=new HashSet<>();
  try {
    byte[] classBytes=loader.getClassBytes(ItemWrench.class.getName());
    ClassNode node=new ClassNode(ASM5);
    ClassReader reader=new ClassReader(classBytes);
    reader.accept(node,ClassReader.EXPAND_FRAMES);
    for (    MethodNode method : node.methods) {
      methods.add(getMethodDesc(method));
    }
  }
 catch (  IOException ignore) {
  }
  ClassWriter cw=new ClassWriter(0);
  MethodVisitor mv;
  String name="String_Node_Str";
  String superName=Type.getInternalName(ItemWrench.class);
  String[] ifaces=ifaceList.toArray(new String[0]);
  cw.visit(V1_6,ACC_PUBLIC | ACC_SUPER,name,null,superName,ifaces);
  cw.visitSource("String_Node_Str",null);
{
    mv=cw.visitMethod(ACC_PUBLIC,"String_Node_Str","String_Node_Str",null,null);
    mv.visitCode();
    mv.visitVarInsn(ALOAD,0);
    mv.visitMethodInsn(INVOKESPECIAL,superName,"String_Node_Str","String_Node_Str",false);
    mv.visitInsn(RETURN);
    mv.visitMaxs(1,1);
    mv.visitEnd();
  }
  for (  ClassNode node : nodes) {
    for (    MethodNode method : node.methods) {
      String mn=getMethodDesc(method);
      if (methods.contains(mn))       continue;
      methods.add(mn);
      Type returnType=Type.getReturnType(method.desc);
      int returnOpCode=returnType.getOpcode(IRETURN);
      mv=cw.visitMethod(ACC_PUBLIC,method.name,method.desc,null,null);
      mv.visitCode();
switch (returnOpCode) {
case RETURN:
        break;
case IRETURN:
      mv.visitInsn(returnType == Type.BOOLEAN_TYPE ? ICONST_1 : ICONST_0);
    break;
case LRETURN:
  mv.visitInsn(LCONST_0);
break;
case FRETURN:
mv.visitInsn(FCONST_0);
break;
case DRETURN:
mv.visitInsn(DCONST_0);
break;
case ARETURN:
mv.visitInsn(ACONST_NULL);
break;
}
mv.visitInsn(returnOpCode);
mv.visitInsn(RETURN);
mv.visitMaxs(returnOpCode != RETURN ? 1 : 0,1 + Type.getArgumentTypes(method.desc).length);
mv.visitEnd();
}
}
cw.visitEnd();
Class<?> ret=(new ASMClassLoader()).define(name,cw.toByteArray());
try {
return (ItemWrench)ret.newInstance();
}
 catch (Throwable e) {
throw new RuntimeException(e);
}
}