code: public static boolean isValidValue(JsonReader in) throws IOException {
          if (in.peek() == JsonToken.NULL) {
              in.skipValue();
              return false;
          }
          return true;
      }
docs: Determines whether the next value within the reader is not null.
  
  @param in the json reader used to read the stream
  @return true if a valid value exists, or false if the value is null.
  @throws IOException see {@link JsonReader#skipValue()}