public function whereEmpty($conditions) {
		// if provided conditions are an array
		if(is_array($conditions)) {
			// for each condition
			foreach($conditions as $column) {
				// add the condition
				$this->whereEmpty($column);
			}
		}
		else {
			// secure the column name
			list(
				$column, 
				$placeholder
			) = Convert::columnToPlaceholder($this->Quote ,$conditions);
			// save the condition
			$this->Conditions[] = "{$this->Operator} ( {$column} == :empty_{$placeholder} OR {$column} IS NULL )";
			// add the empty value
			$this->Values[":empty_{$placeholder}"] = '';
		}
		// return self to the next method
		return $this;
	}