MBS-12351: Also trim space only disambiguations

The transform was not being applied on spaces-only
disambiguation fields, because FormHandler considers it
empty. As such, I added validate_when_empty to enforce
always running the transform on the comment field.

This broke the test adding a rel, because we weren't entering
the comment field. That seemed weird to begin with (we are also
not changing name and sort name, yet we list them) so adding it here.

lib/MusicBrainz/Server/Form/Field/Comment.pm

@@ -6,6 +6,9 @@ extends 'HTML::FormHandler::Field::Text';
 
 has '+maxlength' => ( default => 255 );
 has '+not_nullable' => ( default => 1 );
+has '+validate_when_empty' => (
+    default => 1
+);
 
 apply ([
     {

t/lib/t/MusicBrainz/Server/Controller/Artist/Create.pm

@@ -275,6 +275,41 @@ test 'MBS-10976: Private use characters U+E000..U+F8FF are allowed' => sub {
     );
 };
 
+test 'MBS-12351: Space-only disambiguations are trimmed properly' => sub {
+    my $test = shift;
+    my $mech = $test->mech;
+
+    prepare_test($test);
+
+    $mech->get_ok('/artist/create');
+
+    my @edits = capture_edits {
+        $mech->submit_form_ok({
+            with_fields => {
+                'edit-artist.name' => 'Testy',
+                'edit-artist.sort_name' => 'Testy',
+                'edit-artist.comment' => '   ',
+            },
+        },
+        'The form returned a 2xx response code')
+    } $test->c;
+
+    ok(
+        $mech->uri =~ $artist_page_regexp,
+        'The user is redirected to the artist page after entering the edit',
+    );
+
+    is(@edits, 1, 'The edit was entered');
+
+    my $edit = shift(@edits);
+
+    is(
+        $edit->data->{comment},
+        '',
+        'The submitted comment is empty',
+    );
+};
+
 sub prepare_test {
     my $test = shift;
 

t/lib/t/MusicBrainz/Server/Controller/Artist/EditRelationships.pm

@@ -35,6 +35,7 @@ test 'Test adding a relationship' => sub {
         $mech->post('/artist/745c079d-374e-4436-9448-da92dedef3ce/edit', {
             'edit-artist.name' => 'Test Artist',
             'edit-artist.sort_name' => 'Artist, Test',
+            'edit-artist.comment' => 'Yet Another Test Artist',
             'edit-artist.type_id' => '1',
             'edit-artist.gender_id' => '1',
             'edit-artist.period.ended' => '1',