docs: public Number optNumber(String key, Number defaultValue) {
          Object val = this.opt(key);
          if (NULL.equals(val)) {
              return defaultValue;
          }
          if (val instanceof Number){
              return (Number) val;
          }
          
          try {
              return stringToNumber(val.toString());
          } catch (Exception e) {
              return defaultValue;
          }
      }