You're assuming new Fl ('Myflash.swf') does not fail, and that it returns something in list context. It does fail, and it returns nothing.

$ cat junk.pl
#!/usr/bin/perl --

use strict;
use warnings;

sub Fl::new {  return }

my $url ;
my %swf = ('file' => new Fl ('Myflash.swf'), 'url' => $url);

use Data::Dumper;
print Dumper( \%swf );

__END__

$ perl junk.pl
Odd number of elements in hash assignment at junk.pl line 9.
Use of uninitialized value $url in list assignment at junk.pl line 9.
$VAR1 = {
          '' => undef,
          'file' => 'url'
        };

$
$ cat junk2.pl
#!/usr/bin/perl --

use strict;
use warnings;

sub Fl::new {  return }

my $url ;
my %swf = ('file' => scalar new Fl ('Myflash.swf'), 'url' => $url);

use Data::Dumper;
print Dumper( \%swf );

__END__

$ perl junk2.pl
$VAR1 = {
          'url' => undef,
          'file' => undef
        };
[download]

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