@Override
        public String toString() {
            if (Objects.isNull(format)) {
                return val.toString();
            }
            return String.format(format, val);
        }
how to json this Object?
com.fasterxml.jackson.databind.ser.std.NumberSerializer#serialize
shenyu-plugin/shenyu-plugin-mock/src/main/java/org/apache/shenyu/plugin/mock/util/MockUtil.java