code: public boolean addHarvester(CandidateHarvester harvester) {
  		CandidateType candidateType = harvester.getCandidateType();
  		boolean added = false;
  		synchronized (this.harvesters) {
  			if (!this.harvesters.containsKey(candidateType)) {
  				this.harvesters.put(candidateType, harvester);
  				added = true;
  			} else {
  				added = false;
  			}
  		}
  		return added;
  	}
docs: Registers a harvester for a certain type of candidates. <b> Only
  <b>one</b> harvester per candidate type is supported.
  
  @param harvester
  The harvester to be registered
  @return Whether the harvester was successfully registered or not.