Null Pointer Exception

V6008 Potential null dereference of ‘dagLock’. QueryTracker.java(557), QueryTracker.java(553)

private void handleFragmentCompleteExternalQuery(QueryInfo queryInfo)
{
  if (queryInfo.isExternalQuery()) 
  {
    ReadWriteLock dagLock = getDagLock(queryInfo.getQueryIdentifier());
    if (dagLock == null) {
      LOG.warn("Ignoring fragment completion for unknown query: {}",
          queryInfo.getQueryIdentifier());
    }
    boolean locked = dagLock.writeLock().tryLock();
    .....
  }
}

A null object is caught, logged, and… the program just keeps running. As a result, the check is followed by a null pointer dereference. Ouch!

The developers must have actually wanted the program to exit the function or throw some special exception in the case of getting a null reference.

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