diff --git a/League/Controllers/AbstractController.cs b/League/Controllers/AbstractController.cs
index 04ec065b..5304ef98 100644
--- a/League/Controllers/AbstractController.cs
+++ b/League/Controllers/AbstractController.cs
@@ -33,9 +33,10 @@ protected JsonResult JsonResponseRedirect(string? redirectUrl)
     /// <returns>Gets the <see cref="System.Security.Claims.ClaimTypes.NameIdentifier"/> of the current user
     /// as <see langword="long"/> integer.</returns>
     [NonAction]
-    protected long GetCurrentUserId()
+    protected long? GetCurrentUserId()
     {
-        return long.Parse(User.Claims.First(c => c.Type == System.Security.Claims.ClaimTypes.NameIdentifier).Value);
+        var userId = User.Claims.FirstOrDefault(c => c.Type == System.Security.Claims.ClaimTypes.NameIdentifier)?.Value;
+        return long.TryParse(userId, out var id) ? id : null;
     }
 
     /// <summary>
diff --git a/League/Controllers/Match.cs b/League/Controllers/Match.cs
index 2a1f1781..f8f54e60 100644
--- a/League/Controllers/Match.cs
+++ b/League/Controllers/Match.cs
@@ -84,9 +84,12 @@ public IActionResult Index()
     [HttpGet("[action]")]
     public async Task<IActionResult> Fixtures(CancellationToken cancellationToken)
     {
+        var tournament = await GetPlanTournament(cancellationToken);
+        if (tournament == null) return NotFound();
+
         var model = new FixturesViewModel(_timeZoneConverter)
         {
-            Tournament = await GetPlanTournament(cancellationToken),
+            Tournament = tournament,
             PlannedMatches = await _appDb.MatchRepository.GetPlannedMatchesAsync(
                 new PredicateExpression(PlannedMatchFields.TournamentId == _tenantContext.TournamentContext.MatchPlanTournamentId), cancellationToken),
             // try to use the browser cookie
@@ -203,11 +206,12 @@ public async Task<IActionResult> PublicCalendar(long? team, long? round, Cancell
     [HttpGet("[action]")]
     public async Task<IActionResult> Results(CancellationToken cancellationToken)
     {
+        var tournament = await GetResultTournament(cancellationToken);
+        if (tournament == null) return NotFound();
+
         var model = new ResultsViewModel(_timeZoneConverter)
         {
-            Tournament =
-                await _appDb.TournamentRepository.GetTournamentAsync(new PredicateExpression(TournamentFields.Id == _tenantContext.TournamentContext.MatchResultTournamentId),
-                    cancellationToken),
+            Tournament = tournament,
             CompletedMatches = await _appDb.MatchRepository.GetCompletedMatchesAsync(
                 new PredicateExpression(CompletedMatchFields.TournamentId == _tenantContext.TournamentContext.MatchResultTournamentId), cancellationToken),
             // try to use the browser cookie
@@ -565,6 +569,17 @@ private static MatchEntity FillMatchEntity(PlannedMatchRow currentData)
         return null;
     }
 
+    private async Task<TournamentEntity?> GetResultTournament(CancellationToken cancellationToken)
+    {
+        var tournament =
+            await _appDb.TournamentRepository.GetTournamentAsync(new PredicateExpression(TournamentFields.Id == _tenantContext.TournamentContext.MatchResultTournamentId), cancellationToken);
+
+        if (tournament != null) return tournament;
+
+        _logger.LogCritical("{name} '{id}' does not exist. User ID '{currentUser}'.", nameof(_tenantContext.TournamentContext.MatchResultTournamentId), _tenantContext.TournamentContext.MatchPlanTournamentId, GetCurrentUserId());
+        return null;
+    }
+
     private async Task<EnterResultViewModel> GetEnterResultViewModel(MatchEntity match, CancellationToken cancellationToken)
     {
         match.Sets.RemovedEntitiesTracker = new EntityCollection<SetEntity>();
@@ -646,7 +661,7 @@ private void SendFixtureNotification(long matchId)
             Parameters =
             {
                 CultureInfo = CultureInfo.DefaultThreadCurrentUICulture ?? CultureInfo.CurrentCulture,
-                ChangedByUserId = GetCurrentUserId(),
+                ChangedByUserId = GetCurrentUserId() ?? throw new InvalidOperationException("Current user ID must not be null"),
                 MatchId = matchId,
             }
         });
@@ -663,7 +678,7 @@ private void SendResultNotification(in MatchEntity match)
             Parameters =
             {
                 CultureInfo = CultureInfo.DefaultThreadCurrentUICulture ?? CultureInfo.CurrentCulture,
-                ChangedByUserId = GetCurrentUserId(),
+                ChangedByUserId = GetCurrentUserId() ?? throw new InvalidOperationException("Current user ID must not be null"),
                 Match = match,
             }
         });
diff --git a/League/Controllers/Ranking.cs b/League/Controllers/Ranking.cs
index f129e3fa..613df1ab 100644
--- a/League/Controllers/Ranking.cs
+++ b/League/Controllers/Ranking.cs
@@ -63,7 +63,8 @@ await _appDb.TournamentRepository.GetTournamentAsync(new PredicateExpression(Tou
 
             if (model.Tournament == null)
             {
-                throw new Exception($"{nameof(_tenantContext.TournamentContext.MatchResultTournamentId)} '{_tenantContext.TournamentContext.MatchResultTournamentId}' does not exist");
+                _logger.LogCritical("{name} '{id}' does not exist. User ID '{currentUser}'.", nameof(_tenantContext.TournamentContext.MatchPlanTournamentId), _tenantContext.TournamentContext.MatchResultTournamentId, GetCurrentUserId());
+                return NotFound();
             }
 
             return View(Views.ViewNames.Ranking.Table, model);
@@ -71,7 +72,7 @@ await _appDb.TournamentRepository.GetTournamentAsync(new PredicateExpression(Tou
         catch (Exception e)
         {
             _logger.LogCritical(e, "Error when creating the ranking table");
-            throw;
+            return NotFound();
         }
     }
 
diff --git a/League/Controllers/TeamApplication.cs b/League/Controllers/TeamApplication.cs
index b6145240..d93639fd 100644
--- a/League/Controllers/TeamApplication.cs
+++ b/League/Controllers/TeamApplication.cs
@@ -525,7 +525,7 @@ public async Task<IActionResult> Confirm(bool done, CancellationToken cancellati
                         TeamId = teamInRoundEntity.TeamId,
                         IsNewApplication = isNewApplication,
                         RoundId = teamInRoundEntity.RoundId,
-                        RegisteredByUserId = GetCurrentUserId(),
+                        RegisteredByUserId = GetCurrentUserId() ?? throw new InvalidOperationException("Current user ID must not be null"),
                         UrlToEditApplication = TenantLink.ActionLink(nameof(EditTeam), nameof(TeamApplication), new { teamId = teamInRoundEntity.TeamId }, scheme: Request.Scheme, host: Request.Host) ?? string.Empty
                     }
                 });
@@ -697,11 +697,6 @@ private async Task<ApplicationSessionModel> GetNewSessionModel(CancellationToken
         var previousTournament = await _appDb.TournamentRepository.GetTournamentAsync(
             new PredicateExpression(TournamentFields.NextTournamentId == _tenantContext.TournamentContext.ApplicationTournamentId),
             cancellationToken);
-        if (previousTournament == null)
-        {
-            _logger.LogCritical("No tournament found for ID '{ApplicationTournamentId}'", _tenantContext.TournamentContext.ApplicationTournamentId);
-            throw new InvalidOperationException($"No tournament found for ID '{_tenantContext.TournamentContext.ApplicationTournamentId}'");
-        }
         
         return new ApplicationSessionModel
         {
@@ -709,7 +704,7 @@ private async Task<ApplicationSessionModel> GetNewSessionModel(CancellationToken
             Team = new TeamEditorComponentModel {HtmlFieldPrefix = nameof(ApplicationSessionModel.Team), IsNew = true},
             Venue = new VenueEditorComponentModel {HtmlFieldPrefix = nameof(ApplicationSessionModel.Venue), IsNew = true},
             TournamentName = teamApplicationTournament.Name,
-            PreviousTournamentId = previousTournament.Id
+            PreviousTournamentId = previousTournament?.Id
         };
     }
 
@@ -741,7 +736,7 @@ private async Task AddManagerToTeamEntity(TeamEntity teamEntity, CancellationTok
         {
             var mot = teamEntity.ManagerOfTeams.AddNew();
             mot.Team = teamEntity;
-            mot.UserId = GetCurrentUserId();
+            mot.UserId = GetCurrentUserId() ?? throw new InvalidOperationException("Current user ID must not be null");
         }
         else
         {
@@ -752,7 +747,7 @@ private async Task AddManagerToTeamEntity(TeamEntity teamEntity, CancellationTok
             {
                 mot = teamEntity.ManagerOfTeams.AddNew();
                 mot.TeamId = teamEntity.Id;
-                mot.UserId = GetCurrentUserId();
+                mot.UserId = GetCurrentUserId() ?? throw new InvalidOperationException("Current user ID must not be null");
             }
         }
     }