Tools - Make Entities and Repositories nullable (#3313)

* support nullability in tools' entities and repositories

* enables C# nullability checks in these files
* includes documentation for affected files

* refine documentation per code review

* improve comments on SendFileData structure

* fix ReferenceEvent.MaxAccessCount documentation

* add value notation to SendFileData.FileName

src/Core/Tools/Repositories/ISendRepository.cs

@@ -1,10 +1,36 @@
-using Bit.Core.Repositories;
+#nullable enable
+
+using Bit.Core.Repositories;
 using Bit.Core.Tools.Entities;
 
 namespace Bit.Core.Tools.Repositories;
 
+/// <summary>
+/// Service for saving and loading <see cref="Send"/>s in persistent storage.
+/// </summary>
 public interface ISendRepository : IRepository<Send, Guid>
 {
+    /// <summary>
+    /// Loads all <see cref="Send"/>s created by a user.
+    /// </summary>
+    /// <param name="userId">
+    /// Identifies the user.
+    /// </param>
+    /// <returns>
+    /// A task that completes once the <see cref="Send"/>s have been loaded.
+    /// The task's result contains the loaded <see cref="Send"/>s.
+    /// </returns>
     Task<ICollection<Send>> GetManyByUserIdAsync(Guid userId);
+
+    /// <summary>
+    /// Loads <see cref="Send"/>s scheduled for deletion.
+    /// </summary>
+    /// <param name="deletionDateBefore">
+    /// Load sends whose <see cref="Send.DeletionDate" /> is &lt; this date.
+    /// </param>
+    /// <returns>
+    /// A task that completes once the <see cref="Send"/>s have been loaded.
+    /// The task's result contains the loaded <see cref="Send"/>s.
+    /// </returns>
     Task<ICollection<Send>> GetManyByDeletionDateAsync(DateTime deletionDateBefore);
 }