lost in subtype coersion

[Jiří Pavlovský]

Hello,

I'm trying to apply some processing on an attribute value when it is 
set. I thought creating custom subtype and a coercion is the way to do 
it, but cannot figure it out.
The coersion is not run.
See my code below.
What am I doing wrong?
I need this filtering to appear seamlessly on the subject attribute due 
to backwards compatibility.


subtype 'Subject'
=> as 'Str';

coerce 'Subject'
=> from 'Str'
=> via {

    my $sanitized = sanitize_input($_);
    $sanitized;

};

subtype MaybeSubject => as 'Maybe[Subject]';
coerce 'MaybeSubject'
=> from 'Subject'
=> via {
   my $sanitized =sanitize_input($_);
    $sanitized;

};

has 'subject' => (
  is         => 'rw',
  isa        => 'MaybeSubject',
  predicate  => 'has_subject',
  coerce     => 1,
);