Annotate the remainder of metadata for nullability

src/EFCore.Relational/Metadata/IConventionDbFunction.cs

@@ -29,11 +29,6 @@ public interface IConventionDbFunction : IConventionAnnotatable, IDbFunction
         /// <exception cref="InvalidOperationException"> If the function has been removed from the model. </exception>
         new IConventionDbFunctionBuilder Builder { get; }
 
-        /// <summary>
-        ///     Indicates whether this function is in a model, i.e. hasn't been removed from one.
-        /// </summary>
-        new bool IsInModel { get; }
-
         /// <summary>
         ///     Gets the configuration source for this function.
         /// </summary>

src/EFCore.Relational/Metadata/IConventionSequence.cs

@@ -26,11 +26,6 @@ public interface IConventionSequence : ISequence, IConventionAnnotatable
         /// <exception cref="InvalidOperationException"> If the sequence has been removed from the model. </exception>
         new IConventionSequenceBuilder Builder { get; }
 
-        /// <summary>
-        ///     Indicates whether this sequence is in a model, i.e. hasn't been removed from one.
-        /// </summary>
-        new bool IsInModel { get; }
-
         /// <summary>
         ///     Gets the configuration source for this <see cref="IConventionSequence" />.
         /// </summary>

src/EFCore/Metadata/Builders/CollectionNavigationBuilder.cs

@@ -225,13 +225,12 @@ private InternalForeignKeyBuilder WithOneBuilder(MemberIdentity reference)
         /// <returns> An object to further configure the relationship. </returns>
         public virtual CollectionCollectionBuilder WithMany([NotNull] string navigationName)
         {
-            if (Builder != null
-                && Builder.Metadata.PrincipalToDependent == null)
+            if (Builder?.Metadata.PrincipalToDependent == null)
             {
                 throw new InvalidOperationException(
                     CoreStrings.MissingInverseManyToManyNavigation(
-                        Builder.Metadata.PrincipalEntityType.DisplayName(),
-                        Builder.Metadata.DeclaringEntityType.DisplayName()));
+                        Builder?.Metadata.PrincipalEntityType.DisplayName(),
+                        Builder?.Metadata.DeclaringEntityType.DisplayName()));
             }
 
             var leftName = Builder?.Metadata.PrincipalToDependent!.Name;
@@ -322,7 +321,7 @@ protected virtual IMutableSkipNavigation WithLeftManyNavigation([NotNull] string
         ///     doing so can result in application failures when updating to a new Entity Framework Core release.
         /// </summary>
         [EntityFrameworkInternal]
-        protected virtual IMutableSkipNavigation WithRightManyNavigation([NotNull] string navigationName, [CanBeNull] string? inverseName)
+        protected virtual IMutableSkipNavigation WithRightManyNavigation([NotNull] string navigationName, [NotNull] string inverseName)
             => WithRightManyNavigation(MemberIdentity.Create(navigationName), inverseName);
 
         /// <summary>

src/EFCore/Metadata/Builders/CollectionNavigationBuilder`.cs

@@ -94,9 +94,17 @@ public virtual ReferenceCollectionBuilder<TEntity, TRelatedEntity> WithOne(
         ///     The name of the collection navigation property on the other end of this relationship.
         /// </param>
         /// <returns> An object to further configure the relationship. </returns>
-        public new virtual CollectionCollectionBuilder<TRelatedEntity, TEntity> WithMany([NotNull] string navigationName)
+        public new virtual CollectionCollectionBuilder<TRelatedEntity, TEntity>? WithMany([NotNull] string navigationName)
         {
-            var leftName = Builder?.Metadata.PrincipalToDependent!.Name;
+            if (Builder?.Metadata.PrincipalToDependent == null)
+            {
+                throw new InvalidOperationException(
+                    CoreStrings.MissingInverseManyToManyNavigation(
+                        Builder?.Metadata.PrincipalEntityType.DisplayName(),
+                        Builder?.Metadata.DeclaringEntityType.DisplayName()));
+            }
+
+            var leftName = Builder.Metadata.PrincipalToDependent.Name;
             var collectionCollectionBuilder =
                 new CollectionCollectionBuilder<TRelatedEntity, TEntity>(
                     RelatedEntityType,

src/EFCore/Metadata/Conventions/IConventionBatch.cs

@@ -25,10 +25,9 @@ public interface IConventionBatch : IDisposable
         /// </summary>
         /// <param name="foreignKey"> The foreign key to track. </param>
         /// <returns>
-        ///     An object that will contain the reference to the new foreign key instance
-        ///     if the given one was replaced by a convention.
+        ///     An object that will contain the reference to the new foreign key instance if the given one was replaced by a convention.
+        ///     Otherwise, returns the original foreign key.
         /// </returns>
-        // TODO-NULLABLE: does this ever refer null (as is implied by the comment?)
         IMetadataReference<IConventionForeignKey> Track([NotNull] IConventionForeignKey foreignKey);
     }
 }

src/EFCore/Metadata/Internal/InternalPropertyBuilder.cs

@@ -580,10 +580,10 @@ public virtual bool CanSetKeyValueComparer([CanBeNull] ValueComparer? comparer,
         ///     any release. You should only use it directly in your code with extreme caution and knowing that
         ///     doing so can result in application failures when updating to a new Entity Framework Core release.
         /// </summary>
-        public virtual InternalPropertyBuilder Attach([NotNull] InternalEntityTypeBuilder entityTypeBuilder)
+        public virtual InternalPropertyBuilder? Attach([NotNull] InternalEntityTypeBuilder entityTypeBuilder)
         {
             var newProperty = entityTypeBuilder.Metadata.FindProperty(Metadata.Name);
-            InternalPropertyBuilder newPropertyBuilder;
+            InternalPropertyBuilder? newPropertyBuilder;
             var configurationSource = Metadata.GetConfigurationSource();
             var typeConfigurationSource = Metadata.GetTypeConfigurationSource();
             if (newProperty != null
@@ -605,10 +605,15 @@ public virtual InternalPropertyBuilder Attach([NotNull] InternalEntityTypeBuilde
 
                 newPropertyBuilder = identifyingMemberInfo == null
                     ? entityTypeBuilder.Property(
-                        Metadata.ClrType, Metadata.Name, Metadata.GetTypeConfigurationSource(), configurationSource)!
+                        Metadata.ClrType, Metadata.Name, Metadata.GetTypeConfigurationSource(), configurationSource)
                     : (identifyingMemberInfo as PropertyInfo)?.IsIndexerProperty() == true
-                        ? entityTypeBuilder.IndexerProperty(Metadata.ClrType, Metadata.Name, configurationSource)!
-                        : entityTypeBuilder.Property(identifyingMemberInfo, configurationSource!)!;
+                        ? entityTypeBuilder.IndexerProperty(Metadata.ClrType, Metadata.Name, configurationSource)
+                        : entityTypeBuilder.Property(identifyingMemberInfo, configurationSource!);
+
+                if (newPropertyBuilder is null)
+                {
+                    return null;
+                }
             }
 
             if (newProperty == Metadata)