Fix last build errors

src/Umbraco.Core/Persistence/Repositories/IContentTypeRepositoryBase.cs

@@ -11,7 +11,7 @@ namespace Umbraco.Cms.Core.Persistence.Repositories
     public interface IContentTypeRepositoryBase<TItem> : IReadWriteQueryRepository<int, TItem>, IReadRepository<Guid, TItem>
         where TItem : IContentTypeComposition
     {
-        TItem Get(string alias);
+        TItem? Get(string alias);
         IEnumerable<MoveEventInfo<TItem>> Move(TItem moving, EntityContainer container);
 
         /// <summary>

src/Umbraco.Core/Persistence/Repositories/IKeyValueRepository.cs

@@ -10,6 +10,6 @@ namespace Umbraco.Cms.Core.Persistence.Repositories
         /// </summary>
         /// <param name="keyPrefix"></param>
         /// <returns></returns>
-        IReadOnlyDictionary<string, string>? FindByKeyPrefix(string keyPrefix);
+        IReadOnlyDictionary<string, string?>? FindByKeyPrefix(string keyPrefix);
     }
 }