Nullable refernce types refactoring

WotBlitzStatisticsPro.DataAccess/Model/Accounts/AccountInfo.cs

@@ -1,4 +1,7 @@
-using MongoDB.Bson.Serialization.Attributes;
+using System;
+using System.ComponentModel.DataAnnotations;
+using System.Diagnostics.CodeAnalysis;
+using MongoDB.Bson.Serialization.Attributes;
 using WotBlitzStatisticsPro.Common.Model;
 
 namespace WotBlitzStatisticsPro.DataAccess.Model.Accounts
@@ -32,7 +35,8 @@ namespace WotBlitzStatisticsPro.DataAccess.Model.Accounts
         ///<summary>
         /// Player's nick
         ///</summary>
-        public string Nickname { get; set; }
+        [Required]
+        public string Nickname { get; set; } = string.Empty;
 
         ///<summary>
         /// Player information update date

WotBlitzStatisticsPro.DataAccess/Model/Accounts/AccountInfoHistoryKey.cs

@@ -19,14 +19,14 @@ namespace WotBlitzStatisticsPro.DataAccess.Model.Accounts
 
         public int LastBattleTime { get; set; }
 
-        public bool Equals(AccountInfoHistoryKey other)
+        public bool Equals(AccountInfoHistoryKey? other)
         {
             if (ReferenceEquals(null, other)) return false;
             if (ReferenceEquals(this, other)) return true;
             return AccountId == other.AccountId && LastBattleTime == other.LastBattleTime;
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             if (ReferenceEquals(null, obj)) return false;
             if (ReferenceEquals(this, obj)) return true;

WotBlitzStatisticsPro.DataAccess/Model/Accounts/TankInfo.cs

@@ -7,7 +7,7 @@ namespace WotBlitzStatisticsPro.DataAccess.Model.Accounts
     {
         public TankInfo()
         {
-            
+            TankInfoId = new TankInfoKey();
         }
 
         public TankInfo(long accountId, long tankId)

WotBlitzStatisticsPro.DataAccess/Model/Accounts/TankInfoHistory.cs

@@ -7,7 +7,7 @@ namespace WotBlitzStatisticsPro.DataAccess.Model.Accounts
 
         public TankInfoHistory()
         {
-            
+            TankInfoHistoryId = new TankInfoHistoryKey();
         }
 
         public TankInfoHistory(long accountId, long tankId, int lastBattleTime)

WotBlitzStatisticsPro.DataAccess/Model/Accounts/TankInfoHistoryKey.cs

@@ -31,14 +31,14 @@ namespace WotBlitzStatisticsPro.DataAccess.Model.Accounts
         ///</summary>
         public int LastBattleTime { get; set; }
 
-        public bool Equals(TankInfoHistoryKey other)
+        public bool Equals(TankInfoHistoryKey? other)
         {
             if (ReferenceEquals(null, other)) return false;
             if (ReferenceEquals(this, other)) return true;
             return AccountId == other.AccountId && TankId == other.TankId && LastBattleTime == other.LastBattleTime;
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             if (ReferenceEquals(null, obj)) return false;
             if (ReferenceEquals(this, obj)) return true;

WotBlitzStatisticsPro.DataAccess/Model/Accounts/TankInfoKey.cs

@@ -25,14 +25,14 @@ namespace WotBlitzStatisticsPro.DataAccess.Model.Accounts
         ///</summary>
         public long TankId { get; set; }
 
-        public bool Equals(TankInfoKey other)
+        public bool Equals(TankInfoKey? other)
         {
             if (ReferenceEquals(null, other)) return false;
             if (ReferenceEquals(this, other)) return true;
             return AccountId == other.AccountId && TankId == other.TankId;
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             if (ReferenceEquals(null, obj)) return false;
             if (ReferenceEquals(this, obj)) return true;