Don't logout if deviceId is null.

Emby.Server.Implementations/Session/SessionManager.cs

@@ -1540,23 +1540,26 @@ namespace Emby.Server.Implementations.Session
                     Limit = 1
                 }).Items.FirstOrDefault();
 
-            var allExistingForDevice = _authRepo.Get(
-                new AuthenticationInfoQuery
-                {
-                    DeviceId = deviceId
-                }).Items;
-
-            foreach (var auth in allExistingForDevice)
+            if (!string.IsNullOrEmpty(deviceId))
             {
-                if (existing == null || !string.Equals(auth.AccessToken, existing.AccessToken, StringComparison.Ordinal))
-                {
-                    try
+                var allExistingForDevice = _authRepo.Get(
+                    new AuthenticationInfoQuery
                     {
-                        Logout(auth);
-                    }
-                    catch (Exception ex)
+                        DeviceId = deviceId
+                    }).Items;
+
+                foreach (var auth in allExistingForDevice)
+                {
+                    if (existing == null || !string.Equals(auth.AccessToken, existing.AccessToken, StringComparison.Ordinal))
                     {
-                        _logger.LogError(ex, "Error while logging out.");
+                        try
+                        {
+                            Logout(auth);
+                        }
+                        catch (Exception ex)
+                        {
+                            _logger.LogError(ex, "Error while logging out.");
+                        }
                     }
                 }
             }