open3: Can't call method "close" on an undefined value at C:/perl/lib/IPC/Open3.pm line 368.

open3: Can't call method "close" on an undefined value at C:/perl/lib/IPC/Open3.pm line 368.

    while executing
"::perl::CODE(0x18627b4)"
    invoked from within
".b invoke "
    invoked from within
".b instate {pressed !disabled} { .b state !pressed; .b invoke } "
    (command bound to event)

##</code><code>##

use strict;

use Tkx;
use IPC::Open3;

my $mw = Tkx::widget->new('.');
my $tw = $mw->new_text();

my $bt = $mw->new_ttk__button(
    -text => 'retrieve',
    -command => sub {
        my( $pid, $wtr, $rdr, $err );
        $pid = open3( $wtr, $rdr, $err, 'dir' );
        $tw->insert( 'end', scalar do { local $/; <$rdr> } );
    },
);

Tkx::pack( $tw );
Tkx::pack( $bt );

Tkx::MainLoop;