code: public static InsnList addIntegers(InsnList lhs, InsnList rhs) {
          Validate.notNull(lhs);
          Validate.notNull(rhs);
          
          InsnList ret = new InsnList();
          
          ret.add(lhs);
          ret.add(rhs);
          ret.add(new InsnNode(Opcodes.IADD));
          
          return ret;
      }
docs: Adds two integers together and puts the result on to the stack.
  @param lhs instructions to generate the first operand -- must leave an int on the stack
  @param rhs instructions to generate the second operand -- must leave an int on the stack
  @return instructions to add the two numbers together -- will leave an int on the stack
  @throws NullPointerException if any argument is {@code null}