code: private static InsnList returnDummy(Type returnType) {
          Validate.notNull(returnType);
          Validate.isTrue(returnType.getSort() != Type.METHOD);
  
          InsnList ret = new InsnList();
  
          switch (returnType.getSort()) {
              case Type.VOID:
                  ret.add(new InsnNode(Opcodes.RETURN));
                  break;
              case Type.BOOLEAN:
              case Type.BYTE:
              case Type.SHORT:
              case Type.CHAR:
              case Type.INT:
                  ret.add(new InsnNode(Opcodes.ICONST_0));
                  ret.add(new InsnNode(Opcodes.IRETURN));
                  break;
              case Type.LONG:
                  ret.add(new InsnNode(Opcodes.LCONST_0));
                  ret.add(new InsnNode(Opcodes.LRETURN));
                  break;
              case Type.FLOAT:
                  ret.add(new InsnNode(Opcodes.FCONST_0));
                  ret.add(new InsnNode(Opcodes.FRETURN));
                  break;
              case Type.DOUBLE:
                  ret.add(new InsnNode(Opcodes.DCONST_0));
                  ret.add(new InsnNode(Opcodes.DRETURN));
                  break;
              case Type.OBJECT:
              case Type.ARRAY:
                  ret.add(new InsnNode(Opcodes.ACONST_NULL));
                  ret.add(new InsnNode(Opcodes.ARETURN));
                  break;
              default:
                  throw new IllegalStateException();
          }
  
          return ret;
      }
docs: Generates instructions that returns a dummy value. Return values are as follows:
  <ul>
  <li>void -&gt; no value</li>
  <li>boolean -&gt; false</li>
  <li>byte/short/char/int -&gt; 0</li>
  <li>long -&gt; 0L</li>
  <li>float -&gt; 0.0f</li>
  <li>double -&gt; 0.0</li>
  <li>Object -&gt; null</li>
  </ul>
  
  @param returnType return type of the method this generated bytecode is for
  @return instructions to return a dummy value
  @throws NullPointerException if any argument is {@code null}
  @throws IllegalArgumentException if {@code returnType}'s sort is of {@link Type#METHOD}