public void addHasNext() {
        MethodVisitor mv = super.visitMethod(Opcodes.ACC_PUBLIC, "hasNext", "()Z", null, null);
        mv.visitCode();
        mv.visitVarInsn(Opcodes.ALOAD, 0);
        mv.visitFieldInsn(Opcodes.GETFIELD, "java/util/WeakHashMap$HashIterator", "iter", "Ljava/util/Iterator;");