in reply to Serializing coderefs

I'm trying to do it using B::Utils. Looks like I'm wrong, since this code:
#!/usr/bin/perl my $s = sub { my $k = shift; return $k;}; use B::Utils qw( walkoptree_simple ); print walkoptree_simple( $s, { print } );
issues an error: Can't call method "isa" on unblessed reference looks like B::Utils does not work with coderefs. Any hint?