mn.visitVarInsn(ILOAD, 1);
Label label = new Label();
mn.visitJumpInsn(IFLT, label);
mn.visitVarInsn(ALOAD, 0);
mn.visitVarInsn(ILOAD, 1);
mn.visitFieldInsn(PUTFIELD, "pkg/Bean", "f", "I");
Label end = new Label();
mn.visitJumpInsn(GOTO, end);
mn.visitLabel(label);
mn.visitFrame(F_SAME, 0, null, 0, null);
mn.visitTypeInsn(NEW, "java/lang/IllegalArgumentException");