docs: public static String camelToSnake(String camel, boolean upper) {
          StringBuilder stringBuilder = new StringBuilder();
          for (char c : camel.toCharArray()) {
              char nc = upper ? Character.toUpperCase(c) : Character.toLowerCase(c);
              if (Character.isUpperCase(c)) {
                  stringBuilder.append('_').append(nc);
              } else {
                  stringBuilder.append(nc);
              }
          }
          return stringBuilder.toString();
      }