Nullable annotation fixes for consistency

src/Autofac.Multitenant/ITenantIdentificationStrategy.cs

@@ -19,6 +19,15 @@ public interface ITenantIdentificationStrategy
     /// <see langword="true" /> if the tenant could be identified; <see langword="false" />
     /// if not.
     /// </returns>
+    /// <remarks>
+    /// <para>
+    /// It is technically possible to allow the tenant to be identified but
+    /// still have the tenant ID come out as <see langword="null"/>. If this
+    /// happens, it indicates the strategy has intentionally chosen the "default
+    /// tenant" as the active tenant rather than requiring fallback logic to
+    /// occur.
+    /// </para>
+    /// </remarks>
     [SuppressMessage("Microsoft.Design", "CA1007:UseGenericsWhereAppropriate", Justification = "Tenant identifiers are objects.")]
     bool TryIdentifyTenant(out object? tenantId);
 }

src/Autofac.Multitenant/MultitenantContainer.cs

@@ -395,7 +395,7 @@ private ILifetimeScope CreateTenantScope(object tenantId, Action<ContainerBuilde
     /// <seealso cref="ConfigurationActionBuilder"/>
     /// <seealso cref="ConfigureTenant(object, Action{ContainerBuilder})"/>
     [SuppressMessage("CA1513", "CA1513", Justification = "ObjectDisposedException.ThrowIf is not available in all target frameworks.")]
-    public bool ReconfigureTenant(object tenantId, Action<ContainerBuilder> configuration)
+    public bool ReconfigureTenant(object? tenantId, Action<ContainerBuilder> configuration)
     {
         if (configuration == null)
         {
@@ -488,7 +488,7 @@ public IEnumerable<object> GetTenants()
     /// </summary>
     /// <param name="tenantId">The tenant ID to test.</param>
     /// <returns>If configured, <c>true</c>; otherwise <c>false</c>.</returns>
-    public bool TenantIsConfigured(object tenantId)
+    public bool TenantIsConfigured(object? tenantId)
     {
         tenantId ??= _defaultTenantId;
 
@@ -500,7 +500,7 @@ public bool TenantIsConfigured(object tenantId)
     /// </summary>
     /// <param name="tenantId">The ID of the tenant to dispose.</param>
     /// <returns><c>true</c> if the tenant-collection was modified; otherwise, <c>false</c>.</returns>
-    public bool RemoveTenant(object tenantId)
+    public bool RemoveTenant(object? tenantId)
     {
         tenantId ??= _defaultTenantId;
 

test/Autofac.Multitenant.Test/MultitenantContainerFixture.cs

@@ -317,6 +317,37 @@ public void Resolve_ApplicationLevelSingleton()
         Assert.Same(dep1, dep3);
     }
 
+    [Fact]
+    public void Resolve_DefaultTenantFallbackToApplicationContainer()
+    {
+        var builder = new ContainerBuilder();
+        builder.RegisterType<StubDependency1Impl1>().As<IStubDependency1>();
+        var strategy = new StubTenantIdentificationStrategy()
+        {
+            TenantId = null,
+        };
+        using var mtc = new MultitenantContainer(strategy, builder.Build());
+        Assert.IsType<StubDependency1Impl1>(mtc.Resolve<IStubDependency1>());
+    }
+
+    [Fact]
+    public void Resolve_ResolvesDefaultTenantSpecificRegistrations()
+    {
+        var builder = new ContainerBuilder();
+        builder.RegisterType<StubDependency1Impl1>().As<IStubDependency1>();
+        var strategy = new StubTenantIdentificationStrategy()
+        {
+            TenantId = null,
+        };
+        using var mtc = new MultitenantContainer(strategy, builder.Build());
+        mtc.ConfigureTenant(null, b => b.RegisterType<StubDependency1Impl2>().As<IStubDependency1>());
+        mtc.ConfigureTenant("tenant2", b => b.RegisterType<StubDependency1Impl3>().As<IStubDependency1>());
+
+        Assert.IsType<StubDependency1Impl2>(mtc.Resolve<IStubDependency1>());
+        strategy.TenantId = "tenant2";
+        Assert.IsType<StubDependency1Impl3>(mtc.Resolve<IStubDependency1>());
+    }
+
     [Fact]
     public void Resolve_ResolvesTenantSpecificRegistrations()
     {
@@ -621,12 +652,13 @@ public void GetTenants_CheckRegistered()
             TenantId = "tenant1",
         };
         using var mtc = new MultitenantContainer(strategy, new ContainerBuilder().Build());
+        mtc.ConfigureTenant(null, b => b.RegisterType<StubDependency1Impl1>().AsImplementedInterfaces());
         mtc.ConfigureTenant("tenant1", b => b.RegisterType<StubDependency1Impl1>().AsImplementedInterfaces());
         mtc.ConfigureTenant("tenant2", b => b.RegisterType<StubDependency1Impl2>().AsImplementedInterfaces());
         mtc.ConfigureTenant("tenant3", b => b.RegisterType<StubDependency1Impl3>().AsImplementedInterfaces());
 
         var registeredTenants = mtc.GetTenants().ToList();
-        Assert.Equal(3, registeredTenants.Count);
+        Assert.Equal(4, registeredTenants.Count);
 
         foreach (var tenantId in registeredTenants)
         {