Cannot invoke 'append' with an argument list of type '(String?!)'

Question

I'm trying to add usernames from Parse in an array to display them in a UITableView, but get an error when I'm appending the usernames to my array.

The error I get is: Cannot invoke 'append' with an argument list of type '(String?!)'

What am I doing wrong?

var usernames = [""]

func updateUsers() {      
    var query = PFUser.query()
    query!.whereKey("username", notEqualTo: PFUser.currentUser()!.username!)
    var fetchedUsers = query!.findObjects()

    for fetchedUser in fetchedUsers! {
        self.usernames.append(fetchedUser.username)
    }
}

Solution

I solved my problem. I declare the array as an empty array and for unwrap the optional with the following code:

var usernames = [String]()

self.usernames.removeAll(keepCapacity: true)

    for fetchedUser in fetchedUsers! {
        if let username = fetchedUser.username as String! {
            self.usernames.append(username)
        }
    }