Avoid printf("%s", NULL);

Index: source4/dsdb/samdb/ldb_modules/acl.c
--- source4/dsdb/samdb/ldb_modules/acl.c.orig
+++ source4/dsdb/samdb/ldb_modules/acl.c
@@ -604,7 +604,7 @@ fail:
 		      (int)samAccountName->length, samAccountName->data,
 		      dnsHostName != NULL ? (int)dnsHostName->length : 0,
 		      dnsHostName != NULL ? (const char *)dnsHostName->data : "",
-		      netbios_name, ntds_guid,
+		      netbios_name, ntds_guid  ? ntds_guid : "(NULL)"
 		      forest_name, base_domain);
 	return LDB_ERR_CONSTRAINT_VIOLATION;
 
