$ perl -MData::Dumper -e'@a = split /\t/, "foo\t\tbar"; print Dumper \@a'
$VAR1 = [
          'foo',
          '',
          'bar'
        ];

##</code><code>##

$ perl -MData::Dumper -e'@a = map $_//"NA", split /\t/, "foo\t\tbar"; print Dumper \@a'
$VAR1 = [
          'foo',
          '',
          'bar'
        ];


##</code><code>##

$ perl -MData::Dumper -e'@a = map $_ ne "" ? $_ : "NA", split /\t/, "foo\t\tbar"; print Dumper \@a'
$VAR1 = [
          'foo',
          'NA',
          'bar'
        ];