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

wantarray ? : ;

#!/usr/bin/perl -w

...
sub zero {
    return 0;
}

scalar context _undef == $VAR1 = undef;

...
scalar context nothing == $VAR1 = undef;

list context nothing == $VAR1 = [];

sub routine {
    return undef;
}

sub routine {
    return 0;
}

#!/usr/bin/perl -w

...
sub zero {
    return 0;
}

Benchmark: timing 10000000 iterations of _undef, empty, nothing, zero.
+..
    _undef:  2 wallclock secs ( 0.89 usr + -0.01 sys =  0.88 CPU) @ 11
+363636.36/s  (n=10000000)
     empty:  2 wallclock secs ( 1.09 usr +  0.00 sys =  1.09 CPU) @ 91
+74311.93/s   (n=10000000)
   nothing:  0 wallclock secs ( 0.50 usr +  0.00 sys =  0.50 CPU) @ 20
+000000.00/s  (n=10000000)
      zero:  0 wallclock secs ( 0.06 usr +  0.00 sys =  0.06 CPU) @ 16
+6666666.67/s (n=10000000)

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