diff --git a/Src/Asp.NetCore2/SqlSugar.MongoDbCore/ExpToSql/VisitorItems/FieldPathExtractor.cs b/Src/Asp.NetCore2/SqlSugar.MongoDbCore/ExpToSql/VisitorItems/FieldPathExtractor.cs
index 675314173..fcd6a6171 100644
--- a/Src/Asp.NetCore2/SqlSugar.MongoDbCore/ExpToSql/VisitorItems/FieldPathExtractor.cs
+++ b/Src/Asp.NetCore2/SqlSugar.MongoDbCore/ExpToSql/VisitorItems/FieldPathExtractor.cs
@@ -122,7 +122,7 @@ namespace SqlSugar.MongoDb
             }
             var isJoin = this._context.queryBuilder?.IsSingle()==false;
             var shortName = ((ParameterExpression)expr)?.Name;
-            var joinInfo = this._context.queryBuilder.JoinQueryInfos.FirstOrDefault(it => it.ShortName.EqualCase(shortName));
+            var joinInfo = this._context.queryBuilder?.JoinQueryInfos?.FirstOrDefault(it => it.ShortName.EqualCase(shortName));
             var isObj = false;
             if (joinInfo != null)
             {