allow subtitle not set by providing default value

Author: jjw24

Flow.Launcher.Plugin/Result.cs

@@ -10,9 +10,12 @@ public class Result
     {
 
         private string _pluginDirectory;
+        
         private string _icoPath;
+
         public string Title { get; set; }
-        public string SubTitle { get; set; }
+
+        public string SubTitle { get; set; } = string.Empty;
 
         /// <summary>
         /// This holds the action keyword that triggered the result.