Why these functions are empty?

Hello!
I looked at code in include/linux/module.h and I found empty functions:

static inline void print_modules(void)
{
}

static inline unsigned long module_kallsyms_lookup_name(const char *name)
{
	return 0;
}

static inline int lookup_module_symbol_name(unsigned long addr, char *symna=
me)
{
	return -ERANGE;
}

And why these function haven`t implementation:
static inline int register_module_notifier(struct notifier_block *nb)
{
	/* no events will happen anyway, so this can always succeed */
	return 0;
}

static inline int unregister_module_notifier(struct notifier_block *nb)
{
	return 0;
}

Is module notifier doesn`t exists?