An option of [''] causes an "undefined warning"

[djerius]

Version 0.109.

% perl -MGetopt::Long::Descriptive -E "describe_options( '%o', [''] )"                            
Use of uninitialized value $opt in lc at [...]/Getopt/Long/Descriptive.pm line 533.

This flows from the _expand subroutine, line 326

    316 sub _expand {
    317   my @expanded;
    318 
    319   for my $opt (@_) {
    320     push @expanded, {
    321       spec       => $opt->[0] || '',
    322       desc       => @$opt > 1 ? $opt->[1] : 'spacer',                                            
    323       constraint => $opt->[2] || {},
    324 
    325       # if @$_ is 0 then we got [], a spacer
    326       name       => @$opt ? _munge((split /[:=|!+]/, $opt->[0] || '')[0]) : '',                  
    327     };
    328   }

Namely,

%  perl -E 'say ( defined( (split /[:=|!+]/, "")[0] ) ? "defined" : "undef") '                    
undef