Fix possible NullReferenceException

Author: Jack251970

Flow.Launcher.Plugin/SharedModels/ThemeData.cs

@@ -41,12 +41,16 @@ public ThemeData(string fileNameWithoutExtension, string name, bool? isDark = nu
     /// <inheritdoc />
     public static bool operator ==(ThemeData left, ThemeData right)
     {
+        if (left is null && right is null)
+            return true;
         return left.Equals(right);
     }
 
     /// <inheritdoc />
     public static bool operator !=(ThemeData left, ThemeData right)
     {
+        if (left is null && right is null)
+            return false;
         return !(left == right);
     }