Use guid for seriesId API parameter

Emby.Server.Implementations/TV/TVSeriesManager.cs

@@ -43,9 +43,9 @@ namespace Emby.Server.Implementations.TV
             }
 
             string presentationUniqueKey = null;
-            if (!string.IsNullOrEmpty(query.SeriesId))
+            if (query.SeriesId.HasValue && !query.SeriesId.Value.Equals(default))
             {
-                if (_libraryManager.GetItemById(query.SeriesId) is Series series)
+                if (_libraryManager.GetItemById(query.SeriesId.Value) is Series series)
                 {
                     presentationUniqueKey = GetUniqueSeriesKey(series);
                 }
@@ -93,9 +93,9 @@ namespace Emby.Server.Implementations.TV
 
             string presentationUniqueKey = null;
             int? limit = null;
-            if (!string.IsNullOrEmpty(request.SeriesId))
+            if (request.SeriesId.HasValue && !request.SeriesId.Value.Equals(default))
             {
-                if (_libraryManager.GetItemById(request.SeriesId) is Series series)
+                if (_libraryManager.GetItemById(request.SeriesId.Value) is Series series)
                 {
                     presentationUniqueKey = GetUniqueSeriesKey(series);
                     limit = 1;
@@ -153,7 +153,7 @@ namespace Emby.Server.Implementations.TV
 
             // If viewing all next up for all series, remove first episodes
             // But if that returns empty, keep those first episodes (avoid completely empty view)
-            var alwaysEnableFirstEpisode = !string.IsNullOrEmpty(request.SeriesId);
+            var alwaysEnableFirstEpisode = request.SeriesId.HasValue && !request.SeriesId.Value.Equals(default);
             var anyFound = false;
 
             return allNextUp

Jellyfin.Api/Controllers/TvShowsController.cs

@@ -77,7 +77,7 @@ namespace Jellyfin.Api.Controllers
             [FromQuery] int? startIndex,
             [FromQuery] int? limit,
             [FromQuery, ModelBinder(typeof(CommaDelimitedArrayModelBinder))] ItemFields[] fields,
-            [FromQuery] string? seriesId,
+            [FromQuery] Guid? seriesId,
             [FromQuery] Guid? parentId,
             [FromQuery] bool? enableImages,
             [FromQuery] int? imageTypeLimit,

MediaBrowser.Model/Querying/NextUpQuery.cs

@@ -33,7 +33,7 @@ namespace MediaBrowser.Model.Querying
         /// Gets or sets the series id.
         /// </summary>
         /// <value>The series id.</value>
-        public string SeriesId { get; set; }
+        public Guid? SeriesId { get; set; }
 
         /// <summary>
         /// Gets or sets the start index. Use for paging.