diff --git a/OwnChar/Manager/OwnCharManager.cs b/OwnChar/Manager/OwnCharManager.cs
index 777e060..89d94a2 100644
--- a/OwnChar/Manager/OwnCharManager.cs
+++ b/OwnChar/Manager/OwnCharManager.cs
@@ -2,13 +2,14 @@
 using OwnChar.Manager.Exceptions;
 using OwnChar.Model;
 using Pilz.Cryptography;
+using System.Diagnostics.CodeAnalysis;
 
 namespace OwnChar.Manager;
 
 public class OwnCharManager
 {
     // User
-    public bool IsLoggedIn => CurrentUser != null;
+    public bool IsLoggedIn => CurrentUser != null && DataManager != null;
     public UserAccount? CurrentUser { get; private set; }
 
     // Data Provider
@@ -26,6 +27,7 @@ public class OwnCharManager
         Characters = new(this);
     }
 
+    [MemberNotNull(nameof(CurrentUser), nameof(DataManager))]
     internal protected void CheckLogin()
     {
         if (!IsLoggedIn)
@@ -36,6 +38,7 @@ public class OwnCharManager
     /// Tries to login on the given data provider.
     /// </summary>
     /// <returns>Returns <see cref="true"/> if the login was successfull and <see cref="false"/> if not.</returns>
+    [MemberNotNullWhen(true, nameof(CurrentUser), nameof(DataManager))]
     public bool Login(IDataManager? proxy, string? username, SecureString? password)
     {
         ArgumentNullException.ThrowIfNull(proxy, nameof(proxy));