From a9865367d8aec1bd323680a3440427dfaac2a89b Mon Sep 17 00:00:00 2001
From: Tim Eisele <Ghost_of_Stone@web.de>
Date: Tue, 12 May 2026 18:12:54 +0200
Subject: Safeguard against invalid GUIDs (#16813)

Safeguard against invalid GUIDs
---
 MediaBrowser.Controller/IO/IPathManager.cs              | 16 ++++++++--------
 MediaBrowser.Controller/MediaEncoding/EncodingHelper.cs | 10 ++++++----
 2 files changed, 14 insertions(+), 12 deletions(-)

(limited to 'MediaBrowser.Controller')

diff --git a/MediaBrowser.Controller/IO/IPathManager.cs b/MediaBrowser.Controller/IO/IPathManager.cs
index eb67437545..30961c7610 100644
--- a/MediaBrowser.Controller/IO/IPathManager.cs
+++ b/MediaBrowser.Controller/IO/IPathManager.cs
@@ -22,30 +22,30 @@ public interface IPathManager
     /// <param name="mediaSourceId">The media source id.</param>
     /// <param name="streamIndex">The stream index.</param>
     /// <param name="extension">The subtitle file extension.</param>
-    /// <returns>The absolute path.</returns>
-    public string GetSubtitlePath(string mediaSourceId, int streamIndex, string extension);
+    /// <returns>The absolute path, or <c>null</c> if <paramref name="mediaSourceId"/> is not a valid GUID.</returns>
+    public string? GetSubtitlePath(string mediaSourceId, int streamIndex, string extension);
 
     /// <summary>
     /// Gets the path to the subtitle file.
     /// </summary>
     /// <param name="mediaSourceId">The media source id.</param>
-    /// <returns>The absolute path.</returns>
-    public string GetSubtitleFolderPath(string mediaSourceId);
+    /// <returns>The absolute path, or <c>null</c> if <paramref name="mediaSourceId"/> is not a valid GUID.</returns>
+    public string? GetSubtitleFolderPath(string mediaSourceId);
 
     /// <summary>
     /// Gets the path to the attachment file.
     /// </summary>
     /// <param name="mediaSourceId">The media source id.</param>
     /// <param name="fileName">The attachmentFileName index.</param>
-    /// <returns>The absolute path.</returns>
-    public string GetAttachmentPath(string mediaSourceId, string fileName);
+    /// <returns>The absolute path, or <c>null</c> if <paramref name="mediaSourceId"/> is not a valid GUID.</returns>
+    public string? GetAttachmentPath(string mediaSourceId, string fileName);
 
     /// <summary>
     /// Gets the path to the attachment folder.
     /// </summary>
     /// <param name="mediaSourceId">The media source id.</param>
-    /// <returns>The absolute path.</returns>
-    public string GetAttachmentFolderPath(string mediaSourceId);
+    /// <returns>The absolute path, or <c>null</c> if <paramref name="mediaSourceId"/> is not a valid GUID.</returns>
+    public string? GetAttachmentFolderPath(string mediaSourceId);
 
     /// <summary>
     /// Gets the chapter images data path.
diff --git a/MediaBrowser.Controller/MediaEncoding/EncodingHelper.cs b/MediaBrowser.Controller/MediaEncoding/EncodingHelper.cs
index 04b13a6f3c..0eeb9e632c 100644
--- a/MediaBrowser.Controller/MediaEncoding/EncodingHelper.cs
+++ b/MediaBrowser.Controller/MediaEncoding/EncodingHelper.cs
@@ -1880,10 +1880,12 @@ namespace MediaBrowser.Controller.MediaEncoding
             var sub2videoParam = enableSub2video ? ":sub2video=1" : string.Empty;
 
             var fontPath = _pathManager.GetAttachmentFolderPath(state.MediaSource.Id);
-            var fontParam = string.Format(
-                CultureInfo.InvariantCulture,
-                ":fontsdir='{0}'",
-                _mediaEncoder.EscapeSubtitleFilterPath(fontPath));
+            var fontParam = fontPath is null
+                ? string.Empty
+                : string.Format(
+                    CultureInfo.InvariantCulture,
+                    ":fontsdir='{0}'",
+                    _mediaEncoder.EscapeSubtitleFilterPath(fontPath));
 
             if (state.SubtitleStream.IsExternal)
             {
-- 
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