$ cat test.pl
use strict;
use Benchmark qw[ cmpthese ];

our @tests = (
    (undef)  x 1000,
    ("")     x 1000,
    (chr(0)) x 1000,
    (0)      x 1000,
    (1)      x 1000,
    ("fred") x 1000,
    );
cmpthese -1, {
    a => q[ !(defined && length() ) and 1 for @tests; ],
    b => q[ !defined || $_ eq ""    and 1 for @tests; ],
    c => q[ ($_ // "") eq ""        and 1 for @tests; ],
    };
$ repeat 5 perl test.pl
    Rate    b    a    c
b 1950/s   -- -18% -33%
a 2379/s  22%   -- -18%
c 2901/s  49%  22%   --
    Rate    b    a    c
b 1950/s   -- -22% -33%
a 2511/s  29%   -- -13%
c 2901/s  49%  16%   --
    Rate    b    a    c
b 1950/s   -- -23% -32%
a 2536/s  30%   -- -12%
c 2875/s  47%  13%   --
    Rate    b    a    c
b 1914/s   -- -22% -32%
a 2466/s  29%   -- -12%
c 2801/s  46%  14%   --
    Rate    b    a    c
b 1950/s   -- -23% -32%
a 2536/s  30%   -- -12%
c 2875/s  47%  13%   --