code: public ReferenceBuilder withPropertyValue(PropertyIdValue propertyIdValue,
  			Value value) {
  		getSnakList(propertyIdValue).add(
  				factory.getValueSnak(propertyIdValue, value));
  		return getThis();
  	}
docs: Adds the given property and value to the constructed reference.
  
  @param propertyIdValue
  the property to add
  @param value
  the value to add
  @return builder object to continue construction