/** @return Candidates map. */
 Map<K, Collection<GridCacheDgcLockCandidate>> candidatesMap() {
   return Collections.unmodifiableMap(map);
 }
 /** @return Near keys. */
 public List<byte[]> nearKeyBytes() {
   return nearKeyBytes != null ? nearKeyBytes : Collections.<byte[]>emptyList();
 }
  /** @throws Exception If failed. */
  public void testEmptyProjections() throws Exception {
    final GridClientCompute dflt = client.compute();

    Collection<? extends GridClientNode> nodes = dflt.nodes();

    assertEquals(NODES_CNT, nodes.size());

    Iterator<? extends GridClientNode> iter = nodes.iterator();

    final GridClientCompute singleNodePrj = dflt.projection(Collections.singletonList(iter.next()));

    final GridClientNode second = iter.next();

    final GridClientPredicate<GridClientNode> noneFilter =
        new GridClientPredicate<GridClientNode>() {
          @Override
          public boolean apply(GridClientNode node) {
            return false;
          }
        };

    final GridClientPredicate<GridClientNode> targetFilter =
        new GridClientPredicate<GridClientNode>() {
          @Override
          public boolean apply(GridClientNode node) {
            return node.nodeId().equals(second.nodeId());
          }
        };

    GridTestUtils.assertThrows(
        log(),
        new Callable<Object>() {
          @Override
          public Object call() throws Exception {
            return dflt.projection(noneFilter).log(-1, -1);
          }
        },
        GridServerUnreachableException.class,
        null);

    GridTestUtils.assertThrows(
        log(),
        new Callable<Object>() {
          @Override
          public Object call() throws Exception {
            return singleNodePrj.projection(second);
          }
        },
        GridClientException.class,
        null);

    GridTestUtils.assertThrows(
        log(),
        new Callable<Object>() {
          @Override
          public Object call() throws Exception {
            return singleNodePrj.projection(targetFilter);
          }
        },
        GridClientException.class,
        null);
  }