private List<User> getFollowers(List<String> followerIds) {
		if (followerIds == null) {
			return emptyList();
		}

		return followerIds.stream()
			.map(userId -> userRepository.findOneByUserId(userId.trim()))
			.filter(Objects::nonNull)
			.collect(toList());
	}
Save user.

@param user include id, userID, fullName, role, password.
@return User
ngrinder-controller/src/main/java/org/ngrinder/user/service/UserService.java