my @userArray = qw(batman robin joker);
my @userArray2; #this is a null array
my @mainArray = (@userArray, @userArray2);

##</code><code>##

#@set should consist "batman robin joker", but not
#"batman robin joker NULL"

##</code><code>##

my @set = map { exists($_)? $_ : delete($_) } @mainArray;