creating custom result type progrmatically

hi

I need to create a  custom result type progrmatically.Following is the code 

ResultItemType resultitemType = new ResultItemType(owner);
            resultitemType.DisplayTemplateUrl = AppConstants.SearchResultTypeNames.SearchResultTypeDisplayTemplate.NewsResultDisplayTemplate;
            resultitemType.Name = "SE1";
            PropertyRuleOperator ruleOperator = new PropertyRuleOperator("Equal", "testing description", "=", false, true, true);
            rule.PropertyName = AppConstants.SearchManagedProperties.ContentTypeId;
            rule.PropertyValues.Add(AppConstants.ContnetTypeNamesAndId.CTNewsId);
            rule.PropertyOperator = ruleOperator;
            resultitemType.Rules = new PropertyRuleCollection();
            resultitemType.Rules.Add(rule);
            resultitemType.DisplayProperties = string.Empty;

            resultitemType.SourceID = new Guid();

Here resultytpe works fine till I don't add my custom propertyruleoperator but as soon as I add the propertyruleoperator  in result type it throws error.

 PropertyRuleOperator ruleOperator = new PropertyRuleOperator("Equal", "testing description", "=", false, true, true);

var item2 = resultItemCollection.FirstOrDefault(x => string.Equals(x.Name, "SE2", StringComparison.OrdinalIgnoreCase)); //resultitemcollection is the collectionof all resulttypes
            item2.Rules.PropertyRules[0].PropertyOperator// using this operator from another source

One more thing when I use propertyruleoperator  from any other existing result source then it works fine.

Why is this issue occuring?Can't we create our own propertyruleoperator object ? propertyruleoperator  class has hidden operators defined so do we need to go for reflection and use this.