Fix NullReferenceException for SelectMany with inline array values

[roji]

Fixes #38285

When using SelectMany with an inline array where the collection values are unreferenced (e.g. e => new[] { "a", "b" }.Select(k => e)), the values in the ValuesExpression had no type mapping inferred from usage context. The postprocessor then wrapped them in a Convert expression with null TypeMapping, causing a NullReferenceException in QuerySqlGenerator.VisitSqlConstant.

Fix: In ApplyTypeMappingsOnValuesExpression, when no type mapping is inferred from usage context, fall back to the default type mapping for the value's CLR type.

Generated SQL (SQL Server):

SELECT [p].[Id], ...
FROM [PrimitiveCollectionsEntity] AS [p]
CROSS APPLY (VALUES (CAST(N'a' AS nvarchar(max))), (N'b')) AS [v]([Value])

[Copilot]

Pull request overview

Fixes a relational query pipeline crash by applying a fallback type mapping to inline VALUES expressions whose value column has no usage-inferred mapping.

Changes:

• Adds default CLR-type mapping fallback in RelationalTypeMappingPostprocessor.
• Adds a shared regression test for SelectMany over unreferenced inline collection values.
• Adds provider-specific expectations for SQL Server and SQLite.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/EFCore.Relational/Query/RelationalTypeMappingPostprocessor.cs	Applies default type mappings to unmapped inline row values when inference is unavailable.
test/EFCore.Specification.Tests/Query/PrimitiveCollectionsQueryTestBase.cs	Adds the shared regression test for issue #38285.
test/EFCore.SqlServer.FunctionalTests/Query/PrimitiveCollectionsQuerySqlServerTest.cs	Adds expected SQL for the new regression test.
test/EFCore.Sqlite.FunctionalTests/Query/PrimitiveCollectionsQuerySqliteTest.cs	Adds SQLite’s expected APPLY-not-supported behavior for the new test.

[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.