fix ChatId operator == :

- true if both chatId are null
- true for different casing username (@channel == @channel)

Author: wiz0u

src/Telegram.Bot/Types/ChatId.cs

@@ -68,12 +68,9 @@ public ChatId(string username)
     /// <summary>Compares two ChatId objects</summary>
     public static bool operator ==(ChatId? obj1, ChatId? obj2)
     {
+        if (ReferenceEquals(obj1, obj2)) return true;
         if (obj1 is null || obj2 is null) return false;
-        if (obj1.Identifier is not null && obj2.Identifier is not null)
-            return obj1.Identifier == obj2.Identifier;
-        if (obj1.Username is not null && obj2.Username is not null)
-            return string.Equals(obj1.Username, obj2.Username, StringComparison.Ordinal);
-        return false;
+        return obj1.Identifier == obj2.Identifier && string.Equals(obj1.Username, obj2.Username, StringComparison.OrdinalIgnoreCase);
     }
 
     /// <summary>Compares two ChatId objects</summary>

test/Telegram.Bot.Tests.Unit/ChatIdTests.cs

@@ -123,7 +123,13 @@ public IEnumerator<object[]> GetEnumerator()
         yield return [new ChatId(50), new ChatId(50), true];
         yield return [new ChatId(100), new ChatId(50), false];
         yield return [new ChatId("@user"), new ChatId("@user"), true];
+        yield return [new ChatId("@user"), new ChatId("@USER"), true];
+        yield return [new ChatId(50), new ChatId("@user"), false];
         yield return [new ChatId(50), new ChatId("@50"), false];
+        yield return [new ChatId(50), new ChatId("50"), true];
+        yield return [new ChatId(50), null!, false];
+        yield return [null!, new ChatId(50), false];
+        yield return [null!, null!, true];
     }
 
     IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();