Passing NULL to variadic function and large memory model

It appears that when using the large memory model results in an invalid pointer.  For example:

void bar(const char *h, ...);

void foo()
{

  bar("Strings:", "String1", "String2", "String3", NULL);

}

void bar(const char *h, ...)

{

  va_list ap;

  const char *ptr;

  va_start(ap, h);

  printf("%s\n", h);

  while( (ptr = va_arg(ap, const char*)) != NULL)
  {

    printf("  %s\n", ptr);

  }

}

Now, looking at the disassembly for foo:

  SUBA    #0x00012,SP           
  MOVX.A  #0x0db22,0x00000(SP)
  MOVX.A  #0x0db2c,0x00004(SP)
  MOVX.A  #0x0db34,0x00008(SP)
  MOVX.A  #0x0db3c,0x0000c(SP)
  CLR.W   0x0010(SP)                        <----- Here's the problem
  CALLA   #.text:bar
  ADDA    #0x00012,SP
  RETA

Note the push of a 16-bit value pushed for the NULL, rather than a 32-bit (well, actually 20-bit) value.  Now when in bar(), 32-bit values are extracted.  And since the upper 16-bits are whatever is on the stack....

So digging around in stdio.h, I see that NULL is just defined as 0.   Now, I understand that this is how it is usually done, but I think that is because it presumes that a pointer size is equal to an integer.  But that isn't the case in the large memory model.

So my solution, thus far, has been to put "--define=NULL="(void *)0"" on the command line.

Have others had this problem?  Is this how they work around the issue?