Error comparing void pointer on HP Itanium

["Radhika M G" <radhika.ganganna@xxxxxxxxxx>]

Hi,

I have this piece of code which compiles on HP11i (HP11.11) machine but
throws error on HP Itanium (HP 11.23). 

#include<stdarg.h>

main()
{
  va_list ptr;

   if(ptr == NULL)
       printf("It works!");
  else
             printf("It does not work!\n");

}

The error thrown on itanium is: 
"rad.c", line 8: error #2041: expression must have arithmetic or pointer
type
    if(ptr == NULL)

What changes do I make in the code so that the code compiles on both HP11.11
and HP11.23? 

Regards,
Radhika