Adding elements in to Map of List of Id

Map<Id, List<Id>> userRoleToUsers = new Map<Id, List<Id>>();

for(User newUser : [SELECT UserRoleId FROM User LIMIT 50000]) {
	if(userRoleToUsers.containsKey(newUser.UserRoleId)) {
		List<Id> usersId = userRoleToUsers.get(newUser.UserRoleId);
		usersId.add(newUser.Id);
		userRoleToUsers.put(newUser.UserRoleId, usersId);
	} else {
		userRoleToUsers.put(newUser.UserRoleId, new List<Id> { newUser.Id });
	}
}