private func fetchUser(withId uid: String) {

    FIRDatabase.database().reference().child("users").child(uid).observeSingleEvent(of: .value, with: { (snapshot) in

        if let dictionary = snapshot.value as? [String: AnyObject] {
            let user = User()
            user.name = dictionary["name"] as? String
            user.profileImageUrl = dictionary["profileImageURL"] as? String
            self.users.append(user)
            self.attemptReloadOfCollection()
        }
    }, withCancel: nil)
}