NULLはゼロだし整数として代入できちゃうよねえって最近のgccは気づいてくれるのすごいな!!

$ cat x.c
#include <stddef.h>
long x = NULL;
$ gcc -c x.c
x.c:2:10: warning: initialization of ‘long int’ from ‘void *’ makes integer from pointer without a cast [-Wint-conversion]
2 | long x = NULL;
| ^~~~