public OfferRequirement(String taskType,Collection<TaskInfo> taskInfos) throws InvalidRequirementException {
  this(taskType,taskInfos,Optional.empty());
}

public OfferRequirement ( String taskType , Collection < TaskInfo > taskInfos ) throws InvalidRequirementException { this ( taskType , taskInfos , Optional . empty ( ) ) ; }
creates a new offerrequirement with empty executor requirement and empty placement constraints .
