BackgroundSource: fix log spam

Author: lenemter

src/Background/BackgroundSource.vala

@@ -116,22 +116,22 @@ public class Gala.BackgroundSource : Object {
         return background;
     }
 
-    private string get_background_path () {
+    private string? get_background_path () {
         if (Drawing.StyleManager.get_instance ().prefers_color_scheme == DARK) {
             var uri = gnome_background_settings.get_string ("picture-uri-dark");
             var path = File.new_for_uri (uri).get_path ();
-            if (FileUtils.test (path, EXISTS)) {
+            if (path != null && FileUtils.test (path, EXISTS)) {
                 return path;
             }
         }
 
         var uri = gnome_background_settings.get_string ("picture-uri");
         var path = File.new_for_uri (uri).get_path ();
-        if (FileUtils.test (path, EXISTS)) {
+        if (path != null && FileUtils.test (path, EXISTS)) {
             return path;
         }
 
-        return uri;
+        return null;
     }
 
     private void background_changed (Background background) {