add nullable enable

src/Core/Vault/Entities/Cipher.cs

@@ -27,10 +27,11 @@ public class Cipher : ITableObject<Guid>, ICloneable
     public string Key { get; set; }
 
     /// <summary>
-    /// Deprecated as of Nov 2025.
+    /// Deprecated as of 2025-11-13.
     /// Source of truth is now CipherArchive (CipherId + UserId).
     /// Kept for backward compatibility during phased migration.
     /// </summary>
+    [Obsolete("Use CipherArchive table instead. This property will be removed in a future release.")]
     public DateTime? ArchivedDate { get; set; }
 
     public void SetNewId()

src/Core/Vault/Entities/CipherArchive.cs

@@ -1,4 +1,6 @@
-using Bit.Core.Entities;
+#nullable enable
+
+using Bit.Core.Entities;
 
 namespace Bit.Core.Vault.Entities;
 

src/Infrastructure.EntityFramework/Vault/Models/CipherArchive.cs

@@ -1,4 +1,4 @@
-using Bit.Infrastructure.EntityFramework.Models;
+#nullable enable
 
 namespace Bit.Infrastructure.EntityFramework.Vault.Models;