code: protected static int indexOf (
          EqualityComparator eqc, Object[] list, Object element)
      {
          requireNotNull(element);
          if (list != null) {
              for (int ii = 0, nn = list.length; ii < nn; ii++) {
                  if (eqc.equals(element, list[ii])) {
                      return ii;
                  }
              }
          }
          return -1;
      }
docs: Helper function for {@link #indexOfRef}, etc.