Make mandatory fields in account, ABSL (In silverlight)

Hi experts,

I created an incident in my customer tenant test because mandatory fields don't work. And they answered me following:

"it's not sufficient to set the field to mandatory in SDK (this only creates the red star), you also have to implement a check using ABSL (i.e. in BeforeSave event).

Hope this clarifies your issue if not please revert back to us.

Thank you for your consideration and cooperation."

But when I tested using ABSL I created an extension called AccountEXT.xbo using the code that you can see in the following image:

The test field was "Country", and when I tried to save the new account, appeared the error that you can see in the following image:

There are someone that know if it exsists another way to set a field (or an extension field) into a mandatory field?

If anyone can help me with this issue, I will be really grateful