Pre built function failure: thisapp.portal.assignUserInProfile();

Hi, I have a function that automates the process of creating an account for customers for the customer portal.

The problem is if a blocked email address is passed through it ends the whole function.

This displays a huge error message and its non-developers that use this function. Is there a way I can handle this fail to display a better message and to also warn the development team on where and why the failure has happened?

A test example of the part of the function thats causing the problem:

string dummy.PractTest(string email)
{

strPortalPractitionerFullAccessProfile = "Practitioner Full Access";

//The error message is caused here when a blocked email is passed through
strCreateResponse = thisapp.portal.assignUserInProfile(email,strPortalPractitionerFullAccessProfile);

   mapCreateResponse = strCreateResponse.toMap();
   checkEmailInput = mapCreateResponse.get("emailId");
   checkProfileInput = mapCreateResponse.get("profileName");

   if(checkEmailInput != null && checkProfileInput != null)
   {
             strMessage = "do somthing";
   }
   else
   {
        /strMessage = "do somthing";
   }
   return strMessage;
}