code: public String getPropertyType(PropertyIdValue propertyIdValue) {
  		if (!datatypes.containsKey(propertyIdValue.getId())) {
  			fetchPropertyInformation(propertyIdValue);
  		}
  		return datatypes.get(propertyIdValue.getId());
  	}
docs: Returns the IRI of the primitive type of an {@link PropertyIdValue}.
  
  @param propertyIdValue
  property whose datatype should be fetched
  @return URI of the datatype of this property, or null if the type could
  not be determined