/** @return Collection of keys that did not pass the filter. */
 public Collection<IgniteTxKey> filterFailedKeys() {
   return filterFailedKeys == null ? Collections.<IgniteTxKey>emptyList() : filterFailedKeys;
 }
 /**
  * Gets pending versions that are less than {@link #version()}.
  *
  * @return Pending versions.
  */
 public Collection<GridCacheVersion> pending() {
   return pending == null ? Collections.<GridCacheVersion>emptyList() : pending;
 }
 /** @return Owned values map. */
 public Map<IgniteTxKey, CacheVersionedValue> ownedValues() {
   return ownedVals == null
       ? Collections.<IgniteTxKey, CacheVersionedValue>emptyMap()
       : Collections.unmodifiableMap(ownedVals);
 }
 /** @return Map of versions to be verified. */
 public Map<IgniteTxKey, GridCacheVersion> dhtVersions() {
   return dhtVers == null ? Collections.<IgniteTxKey, GridCacheVersion>emptyMap() : dhtVers;
 }