package Customer;

  use Devel::Deprecate 'deprecate';

  sub persist {
      my $self         = shift;
      my $change_event = shift || $self->change_event;
      
      deprecate( {
          reason => 'Should no longer have an optional change event',
          warn   => '2008-06-12',   # or DateTime object
          die    => '2008-08-12',   # or DateTime object
          if     => ( scalar @_ ),  # optional?
      } );
      ... rest of method
  }