docs: public static <T> int firstIndexOf(Collection<T> items, Predicate<T> predicate) {
          if (!isEmpty(items)) {
              int index = 0;
              for (T item : items) {
                  if (predicate.apply(item)) {
                      return index;
                  }
  
                  index++;
              }
          }
  
          return NOT_FOUND_INDEX;
      }