sub do_nothing {
 ...
 # return 'nothing'
 return ();
}

##</code><code>##

wantarray ? : ;

##</code><code>##

#!/usr/bin/perl -w

use strict;

use Benchmark;

use Data::Dumper;

my $scalar;
my @list;

my %funcs = (	nothing => \&nothing,
		_undef  => \&_undef,
		empty   => \&empty,
		zero    => \&zero,
	    );

foreach my $func (keys %funcs) {
    no strict 'refs';

    my $scalar = &{$funcs{$func}}();
    print STDERR "scalar context $func == ", Dumper($scalar), "\n";

    my @list = &{$funcs{$func}}();
    print STDERR "list context $func == ", Dumper(\@list), "\n";

}

sub nothing {
    return ;
}

sub _undef {
    return undef;
}

sub empty {
    return ();
}

sub zero {
    return 0;
}

##</code><code>##

scalar context _undef == $VAR1 = undef;

list context _undef == $VAR1 = [
          undef
        ];

scalar context zero == $VAR1 = 0;

list context zero == $VAR1 = [
          0
        ];

scalar context empty == $VAR1 = undef;

list context empty == $VAR1 = [];

scalar context nothing == $VAR1 = undef;

list context nothing == $VAR1 = [];

##</code><code>##

sub routine {
    return undef;
}

##</code><code>##

sub routine {
    return 0;
}

##</code><code>##

#!/usr/bin/perl -w

use strict;

use Benchmark;

use Data::Dumper;

my $scalar;
my @list;

my %funcs = (	nothing => \&nothing,
		_undef  => \&_undef,
		empty   => \&empty,
		zero    => \&zero,
	    );

timethese(10000000, \%funcs);

sub nothing {
    return ;
}

sub _undef {
    return undef;
}

sub empty {
    return ();
}

sub zero {
    return 0;
}

##</code><code>##

Benchmark: timing 10000000 iterations of _undef, empty, nothing, zero...
    _undef:  2 wallclock secs ( 0.89 usr + -0.01 sys =  0.88 CPU) @ 11363636.36/s  (n=10000000)
     empty:  2 wallclock secs ( 1.09 usr +  0.00 sys =  1.09 CPU) @ 9174311.93/s   (n=10000000)
   nothing:  0 wallclock secs ( 0.50 usr +  0.00 sys =  0.50 CPU) @ 20000000.00/s  (n=10000000)
      zero:  0 wallclock secs ( 0.06 usr +  0.00 sys =  0.06 CPU) @ 166666666.67/s (n=10000000)

##</code><code>##

sub build_list {
    my ($arg1, arg2, ...) = @_;

    my @list = ();
    ...
    if (something) {
       return @list;
    } else {
      return ();
    }
}