if (priority.intValue() < 0) {
LOG.error("Priority for execution listener " + executionListener.getClass() + " must be non-negative.");
return;
}
final ExecutionListener previousValue = this.executionListeners.putIfAbsent(priority, executionListener);
if (previousValue != null) {
LOG.error("Cannot register " + executionListener.getClass() + " as an execution listener. Priority "
+ priority.intValue() + " is already taken.");
}