code: public JsonArray add(Object value) {
          if (value == this) {
              throw new IllegalArgumentException("Cannot add self");
          } else if (value == JsonValue.NULL) {
              addNull();
          } else if (checkType(value)) {
              content.add(value);
          } else {
              throw new IllegalArgumentException("Unsupported type for JsonArray: " + value.getClass());
          }
          return this;
      }
docs: Append an element to the {@link JsonArray}.
  
  Note that the type is checked and a {@link IllegalArgumentException} is thrown if not supported.
  
  @param value the value to append.
  @return the {@link JsonArray}.