private void lookupAndProcessPath(MapWork work, Path path,
                           Collection<String> aliasesToOptimize) {
    try {
      boolean isEmpty = Utilities.listNonHiddenFileStatus(physicalContext.getConf(), path).length == 0;
      processPath(work, path, aliasesToOptimize, isEmpty);
    } catch (IOException e) {
      LOG.warn("Could not determine if path {} was empty." +
          "Cannot use null scan optimization for this path.", path, e);
    }
  }
Iterate over all tasks one by one and removes all input paths from task if
conditions as defined in rules match.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/physical/NullScanTaskDispatcher.java