Fix NullReferenceException when it comes to Recommendation in AutoML and CodeGenerator#4774

LittleLittleCloud merged 1 commit intodotnet:masterdotnet/machinelearning:masterfrom

LittleLittleCloud:u/xiaoyun/fixRecommendationBugLittleLittleCloud/machinelearning:u/xiaoyun/fixRecommendationBugCopy head branch name to clipboard