Migrate nullable foreign key to required foreign key

Hi guys,
 
I want to give support for the conversion of nullable foreign key to required foreign key.
 
I got the scenario here below
 

public class CustomSQLGenerator : SqlServerMigrationSqlGenerator
{
	protected override void Generate(AlterColumnOperation alterColumnOperation)
	{
    		var old = (System.Data.Entity.Migrations.Model.AlterColumnOperation)(alterColumnOperation.Inverse)).Column;
    		var column = alterColumnOperation.Column;
 
    		if (column.ClrType == typeof(Guid) && old.IsNullable == null && 
column.IsNullable == false)
    		{
 
    		}
	}
 
}

 
Even that i got the scenario but, i am still not clear what to be done.
 
Guys help me with the solution