Addressing build warnings

Models/Contact.cs

@@ -6,9 +6,9 @@ public class Contact
 {
 #region Properties
     public int ContactID { get; set; }
-    public string Firstname { get; set; }
-    public string Lastname { get; set; }
-    public string PhoneNumber { get; set; }
+    public string? Firstname { get; set; }
+    public string? Lastname { get; set; }
+    public string? PhoneNumber { get; set; }
     public DateTime DateCreated { get; set; }
     public int UserID  { get; set; }
 #endregion

Models/Text.cs

@@ -6,8 +6,8 @@ public class Text
 {
 #region Properties
     public int TextID { get; set; }
-    public string Subject { get; set; }
-    public string Message { get; set; }
+    public string? Subject { get; set; }
+    public string? Message { get; set; }
     public int UserID { get; set; }
     public DateTime DateCreated { get; set; }
 #endregion

Models/TextQueue.cs

@@ -6,8 +6,8 @@ public class TextQueue
 {
 #region Properties
     public int TextQueueID { get; set; }
-    public string Status { get; set; }
-    public string ContactPhoneNumber { get; set; }
+    public string? Status { get; set; }
+    public string? ContactPhoneNumber { get; set; }
     public int TextID { get; set; }
     public int UserID { get; set; }
     public DateTime DateCreated { get; set; }

Repositories/BaseRepository.cs

@@ -1,5 +1,5 @@
 
-using TextSender_API.Repositories;
+namespace TextSender_API.Repositories;
 
 public class BaseRepository
 {

Repositories/UsersRepository.cs

@@ -1,6 +1,3 @@
-using System;
-
-using MongoDB.Bson;
 using MongoDB.Driver;
 
 using TextSender_API.Models;
@@ -100,7 +97,7 @@ public class SaltRepository : BaseRepository
 
     public Salt Retrieve(string userId)
     {
-        return this._bookCollection.Find(s => s.UserId.Equals(userId)).FirstOrDefault();
+        return this._bookCollection.Find(s => s.UserId!.Equals(userId)).FirstOrDefault();
     }
 
     public void Update(Salt salt)