Add regression test for issue#6061

test/EFCore.Cosmos.FunctionalTests/Query/SimpleQueryCosmosTest.cs

@@ -4092,6 +4092,12 @@ public override Task SelectMany_correlated_with_outer_4(bool isAsync)
             return base.SelectMany_correlated_with_outer_4(isAsync);
         }
 
+        [ConditionalTheory(Skip = "Issue#17246")]
+        public override Task FirstOrDefault_over_empty_collection_of_value_type_returns_correct_results(bool isAsync)
+        {
+            return base.FirstOrDefault_over_empty_collection_of_value_type_returns_correct_results(isAsync);
+        }
+
         [ConditionalTheory(Skip = "Issue #17246")]
         public override Task All_client(bool isAsync) => null;
 

test/EFCore.InMemory.FunctionalTests/Query/SimpleQueryInMemoryTest.cs

@@ -280,6 +280,9 @@ public override void Client_code_using_instance_in_anonymous_type()
         [ConditionalTheory(Skip = "Issue #16963")]
         public override Task SelectMany_correlated_with_outer_4(bool isAsync) => null;
 
+        [ConditionalTheory(Skip = "Issue #16963")]
+        public override Task FirstOrDefault_over_empty_collection_of_value_type_returns_correct_results(bool isAsync) => null;
+
         [ConditionalTheory(Skip = "Issue #16963")]
         public override Task All_client(bool isAsync) => null;
 

test/EFCore.Specification.Tests/Query/SimpleQueryTestBase.Select.cs

@@ -1206,5 +1206,16 @@ from o in os.Where(o => c.CustomerID == o.CustomerID)
                             select new { c, o },
                 entryCount: 268);
         }
+
+        [ConditionalTheory] //Issue#6061
+        [MemberData(nameof(IsAsyncData))]
+        public virtual Task FirstOrDefault_over_empty_collection_of_value_type_returns_correct_results(bool isAsync)
+        {
+            return AssertQuery<Customer>(
+                isAsync,
+                cs => from c in cs
+                      where c.CustomerID.Equals("FISSA")
+                      select new { c.CustomerID, OrderId = c.Orders.OrderBy(o => o.OrderID).Select(o => o.OrderID).FirstOrDefault() });
+        }
     }
 }

test/EFCore.SqlServer.FunctionalTests/Query/SimpleQuerySqlServerTest.Select.cs

@@ -1007,5 +1007,19 @@ FROM [Orders] AS [o]
     ORDER BY [c].[City], [o].[OrderID]
 ) AS [t]");
         }
+
+        public override async Task FirstOrDefault_over_empty_collection_of_value_type_returns_correct_results(bool isAsync)
+        {
+            await base.FirstOrDefault_over_empty_collection_of_value_type_returns_correct_results(isAsync);
+
+            AssertSql(
+                @"SELECT [c].[CustomerID], (
+    SELECT TOP(1) [o].[OrderID]
+    FROM [Orders] AS [o]
+    WHERE ([c].[CustomerID] = [o].[CustomerID]) AND [o].[CustomerID] IS NOT NULL
+    ORDER BY [o].[OrderID]) AS [OrderId]
+FROM [Customers] AS [c]
+WHERE [c].[CustomerID] = N'FISSA'");
+        }
     }
 }