static int nfs_idmap_lookup_id(const char *name, size_t namelen, const char *type,
			       __u32 *id, struct idmap *idmap)
{
	char id_str[NFS_UINT_MAXLEN];
	long id_long;
	ssize_t data_size;
	int ret = 0;

	data_size = nfs_idmap_get_key(name, namelen, type, id_str, NFS_UINT_MAXLEN, idmap);
	if (data_size <= 0) {
		ret = -EINVAL;
	} else {
		ret = kstrtol(id_str, 10, &id_long);
		*id = (__u32)id_long;
	}
	return ret;
}

The product dereferences a pointer that it expects to be valid but is NULL.