code: public FilterSpec normalize() {
  		FilterSpec copy = new FilterSpec();
  		copy.attributePath = attributePath;
  		copy.operator = operator;
  		copy.value = value;
  		if (expressions != null) {
  			copy.expressions = cloneExpressions(expressions, true);
  		}
  		return copy;
  	}
docs: Normalizes this FilterSpec by normalizing all FilterSpec objects within
  <code>expressions</code> and then sorting the list itself.
  
  @return normalized FilterSpec