use strict;
use warnings;

use Inline C => Config =>
  TYPEMAPS    => "nullmap.txt",
  BUILD_NOISY => 1,
;

use Inline C =><<'EOC';

typedef unsigned char * unmapped;

unmapped foo(unmapped name) {
  if(name) printf("True\n");
  else printf("False\n");
  return(NULL);
}

unsigned char * bar() {
  return (foo(NULL));
}

EOC

foo(undef);
bar();

__END__
Outputs:
False
False