* @since 12.0
   */
  @Override
  public @Nullable E ceiling(E e) {
    return Iterables.<@Nullable E>getFirst(tailSet(e, true), null);
  }

  /**
   * @since 12.0
   */
  @GwtIncompatible // NavigableSet
  @Override
  public @Nullable E higher(E e) {
    return Iterables.<@Nullable E>getFirst(tailSet(e, false), null);
  }

  @Override
  public E first() {
    return iterator().next();
  }

        final Pair<String, String>[] designJspFileNames = systemHelper.getDesignJspFileNames();
        assertEquals(1, designJspFileNames.length);
        assertEquals("xxx", designJspFileNames[0].getFirst());
        assertEquals("yyy", designJspFileNames[0].getSecond());
    }

    public void test_setForceStop() {
        assertFalse(systemHelper.isForceStop());
        systemHelper.setForceStop(true);

    }

    <T> void clearReferenceQueue(ReferenceQueue<T> referenceQueue) {
      while (referenceQueue.poll() != null) {}
    }

    /** Returns first entry of bin for given hash. */
    @Nullable E getFirst(int hash) {
      // read this volatile field only once
      AtomicReferenceArray<E> table = this.table;
      return table.get(hash & (table.length() - 1));
    }

    }
  }

  /**
   * Returns the next element in {@code iterator} or {@code defaultValue} if the iterator is empty.
   * The {@link Iterables} analog to this method is {@link Iterables#getFirst}.
   *
   * @param defaultValue the default value to return if the iterator is empty
   * @return the next element of {@code iterator} or the default value
   * @since 7.0
   */
  @ParametricNullness