code: public JsonParserBuilder numberHandler(@Nullable NumberHandler numberHandler) {
          checkNoConflict(integerHandler, "integer", numberHandler, "number");
          checkNoConflict(floatingHandler, "floating", numberHandler, "number");
          this.numberHandler = numberHandler;
          return this;
      }
docs: Sets the parser's number value handler, or removes it if {@code null} is passed.
  
  @param numberHandler a new number value handler. {@code null} means there shouldn't be a number value
  handler in the built parser.
  @return a reference to this builder
  @throws java.lang.IllegalStateException if {@link #integerHandler()} or {@link #floatingHandler()} is
  already set