use Dancer2;
set serializer => 'Mutable';
get '/user/:id' => sub {
    my $id   = params->{id};
    return { id => $id, name => 'frank' };
}
dance;


##</code><code>##

 {"id" => 1,"name" => "frank"} did not pass type constraint "Value" (in $self->{"content"})
    "Value" is defined as: (defined($_) and not ref($_)) in /usr/local/share/perl5/Dancer2/Core/App.pm l. 1473