Fix: Prevent crash on fresh startup (#10031)

Author: lukeblevins

src/Files.App/Helpers/AppUpdater.cs

@@ -6,7 +6,7 @@ internal interface ISettingsSerializer
     {
         bool CreateFile(string path);
 
-        string? ReadFromFile();
+        string ReadFromFile();
 
         bool WriteToFile(string? text);
     }

src/Files.App/Serialization/ISettingsSerializer.cs

@@ -21,7 +21,12 @@ public DefaultJsonSettingsDatabase(ISettingsSerializer settingsSerializer, IJson
 
         protected Dictionary<string, object?> GetFreshSettings()
         {
-            var data = SettingsSerializer.ReadFromFile() ?? string.Empty;
+            string data = SettingsSerializer.ReadFromFile();
+
+            if (string.IsNullOrWhiteSpace(data)) 
+            { 
+                data = "null"; 
+            }
 
             return JsonSettingsSerializer.DeserializeFromJson<Dictionary<string, object?>?>(data) ?? new();
         }

src/Files.App/Serialization/Implementation/DefaultJsonSettingsDatabase.cs

@@ -28,7 +28,12 @@ public bool CreateFile(string path)
             return true;
         }
 
-        public string? ReadFromFile()
+        /// <summary>
+        /// Reads a file to a string
+        /// </summary>
+        /// <returns>A string value or string.Empty if nothing is present in the file</returns>
+        /// <exception cref="ArgumentNullException"></exception>
+        public string ReadFromFile()
         {
             _ = _filePath ?? throw new ArgumentNullException(nameof(_filePath));