Fix NullReferenceException for SelectMany with inline array values

src/EFCore.Relational/Query/RelationalTypeMappingPostprocessor.cs

@@ -151,10 +151,23 @@ protected virtual ValuesExpression ApplyTypeMappingsOnValuesExpression(ValuesExp
                     {
                         var value = rowValue.Values[j];
 
-                        if (value.TypeMapping is null
-                            && inferredTypeMappings[j] is { } inferredTypeMapping)
+                        if (value.TypeMapping is null)
                         {
-                            value = _sqlExpressionFactory.ApplyTypeMapping(value, inferredTypeMapping);
+                            if (inferredTypeMappings[j] is { } inferredTypeMapping)
+                            {
+                                value = _sqlExpressionFactory.ApplyTypeMapping(value, inferredTypeMapping);
+                            }
+                            else
+                            {
+                                // No type mapping was inferred from usage context (e.g. SelectMany where the value column isn't
+                                // referenced). Fall back to the default type mapping for the CLR type.
+                                var defaultTypeMapping = RelationalDependencies.TypeMappingSource.FindMapping(
+                                    value.Type, QueryCompilationContext.Model);
+                                if (defaultTypeMapping is not null)
+                                {
+                                    value = _sqlExpressionFactory.ApplyTypeMapping(value, defaultTypeMapping);
+                                }
+                            }
                         }
 
                         // We currently add explicit conversions on the first row (but not to the _ord column), to ensure that the inferred

test/EFCore.Specification.Tests/Query/PrimitiveCollectionsQueryTestBase.cs

@@ -270,6 +270,11 @@ public virtual async Task Inline_collection_in_query_filter()
         Assert.Equal(2, result.Id);
     }
 
+    [ConditionalFact] // #38285
+    public virtual Task Inline_collection_SelectMany_with_unreferenced_collection_value()
+        => AssertQuery(
+            ss => ss.Set<PrimitiveCollectionsEntity>().SelectMany(e => new[] { "a", "b" }.Select(k => e)));
+
     [ConditionalFact]
     public virtual Task Parameter_collection_Count()
     {

test/EFCore.SqlServer.FunctionalTests/Query/PrimitiveCollectionsQuerySqlServerTest.cs

@@ -721,6 +721,18 @@ SELECT COUNT(*)
 """);
     }
 
+    public override async Task Inline_collection_SelectMany_with_unreferenced_collection_value()
+    {
+        await base.Inline_collection_SelectMany_with_unreferenced_collection_value();
+
+        AssertSql(
+            """
+SELECT [p].[Id], [p].[Bool], [p].[Bools], [p].[DateTime], [p].[DateTimes], [p].[Enum], [p].[Enums], [p].[Int], [p].[Ints], [p].[NullableInt], [p].[NullableInts], [p].[NullableString], [p].[NullableStrings], [p].[NullableWrappedId], [p].[NullableWrappedIdWithNullableComparer], [p].[String], [p].[Strings], [p].[WrappedId]
+FROM [PrimitiveCollectionsEntity] AS [p]
+CROSS APPLY (VALUES (CAST(N'a' AS nvarchar(max))), (N'b')) AS [v]([Value])
+""");
+    }
+
     public override async Task Parameter_collection_Count()
     {
         await base.Parameter_collection_Count();

test/EFCore.Sqlite.FunctionalTests/Query/PrimitiveCollectionsQuerySqliteTest.cs

@@ -2053,6 +2053,12 @@ public override async Task Column_collection_SelectMany()
             SqliteStrings.ApplyNotSupported,
             (await Assert.ThrowsAsync<InvalidOperationException>(() => base.Column_collection_SelectMany())).Message);
 
+    public override async Task Inline_collection_SelectMany_with_unreferenced_collection_value()
+        => Assert.Equal(
+            SqliteStrings.ApplyNotSupported,
+            (await Assert.ThrowsAsync<InvalidOperationException>(
+                () => base.Inline_collection_SelectMany_with_unreferenced_collection_value())).Message);
+
     public override async Task Column_collection_SelectMany_with_filter()
         => Assert.Equal(
             SqliteStrings.ApplyNotSupported,