docs: @Override
      public E poll() {
          int h = head;
          @SuppressWarnings("unchecked") E result = (E) elements[h];
          // Element is null if queue empty
          if (result == null)
              return null;
          elements[h] = null;     // Must null out slot
          head = (h + 1) & (elements.length - 1);
          return result;
      }