Fix output name null edge case

CHANGELIST.md

@@ -105,6 +105,7 @@
 - Remove reference to removed file
 - Add README files for two libraries
 - Simplify output name assembly logic
+- Fix output name null edge case
 
 ### 3.2.4 (2024-11-24)
 

MPF.Frontend/ViewModels/MainViewModel.cs

@@ -1421,7 +1421,7 @@ namespace MPF.Frontend.ViewModels
             {
                 // If the previous path is exactly the default path and last filename
                 if (lastDirectory.EndsWith(Path.Combine(defaultOutputPath, lastFilename)))
-                    lastDirectory = Path.GetDirectoryName(lastDirectory);
+                    lastDirectory = Path.GetDirectoryName(lastDirectory) ?? string.Empty;
 
                 // Create the output path
                 if (lastDirectory == defaultOutputPath)