threshold = buffer[k - 1];
    }
    // Up to bufferSize, all elements of buffer are real Ts (not null unless T includes null)
    T[] topK = Arrays.copyOf(castBuffer, bufferSize);
    // we have to support null elements, so no ImmutableList for us
    return unmodifiableList(asList(topK));
  }

        Exception level1 = new IOException("Level 1 error", level2);
        SsoLoginException exception = new SsoLoginException("Top level SSO error", level1);

        assertEquals("Top level SSO error", exception.getMessage());

        // Verify the exception chain
        Throwable cause1 = exception.getCause();
        assertNotNull(cause1);

        Throwable middleCause = new IllegalStateException("Middle cause", rootCause);
        ScheduledJobException exception = new ScheduledJobException("Top level error", middleCause);

        assertEquals("Top level error", exception.getMessage());
        assertEquals(middleCause, exception.getCause());
        assertEquals("Middle cause", exception.getCause().getMessage());

    while (!stack.isEmpty()) {
      // To peek at the top two items, we need to temporarily remove one.
      NodeAndRemainingSuccessors<N> top = stack.removeLast();
      NodeAndRemainingSuccessors<N> prev = stack.peekLast();
      stack.addLast(top);

      N node = top.node;
      N previousNode = prev == null ? null : prev.node;
      if (top.remainingSuccessors == null) {

    while (!stack.isEmpty()) {
      // To peek at the top two items, we need to temporarily remove one.
      NodeAndRemainingSuccessors<N> top = stack.removeLast();
      NodeAndRemainingSuccessors<N> prev = stack.peekLast();
      stack.addLast(top);

      N node = top.node;
      N previousNode = prev == null ? null : prev.node;
      if (top.remainingSuccessors == null) {

        RuntimeException middleCause = new RuntimeException("Middle cause", rootCause);
        FessSystemException topException = new FessSystemException("Top level", middleCause);

        assertEquals("Top level", topException.getMessage());
        assertEquals(middleCause, topException.getCause());
        assertEquals(rootCause, topException.getCause().getCause());
    }

        Throwable intermediateCause = new RuntimeException("Intermediate problem", rootCause);
        GsaConfigException exception = new GsaConfigException("Top level GSA error", intermediateCause);

        assertNotNull(exception);
        assertEquals("Top level GSA error", exception.getMessage());

        // Check first level cause
        assertNotNull(exception.getCause());

        Exception intermediateCause = new IllegalStateException("Intermediate cause", rootCause);
        ScriptEngineException exception = new ScriptEngineException("Top level error", intermediateCause);

        assertEquals("Top level error", exception.getMessage());
        assertEquals(intermediateCause, exception.getCause());
        assertEquals("Intermediate cause", exception.getCause().getMessage());

        Exception middleCause = new IllegalStateException("Middle cause", rootCause);
        DataStoreException exception = new DataStoreException("Top level error", middleCause);

        assertNotNull(exception);
        assertEquals("Top level error", exception.getMessage());
        assertEquals(middleCause, exception.getCause());
        assertEquals(rootCause, exception.getCause().getCause());
    }

        // Test nested exception chain
        Exception rootCause = new IllegalStateException("Root cause");
        Exception middleCause = new RuntimeException("Middle cause", rootCause);
        String message = "Top level error";

        SearchQueryException exception = new SearchQueryException(message, middleCause);

        assertEquals(message, exception.getMessage());
        assertEquals(middleCause, exception.getCause());