Unresolved identifier error 'email' - ios

Question

This is related to a previous question that was solved (See here: Sharing variables). I saw nothing that addresses what to do if your variable still isn't being recognized but your code to pass the variable appears solid.
I'm getting an unresolved identifier error 'email' when attempting to utilize a user's email address as part of a file path to upload an image to Firebase Storage. Code is here:
import UIKit
import Firebase
import MobileCoreServices
import FirebaseStorage
class ThirdViewController: UIViewController {
#IBOutlet weak var uploadButton: UIButton!
#IBOutlet weak var progressView: UIProgressView!
override func viewDidLoad() {
super.viewDidLoad()
self.view.backgroundColor = UIColor(patternImage: UIImage(named:"Book Funnel")!)
// Do any additional setup after loading the view.
}
#IBAction func uploadButtonWasPressed(sender: AnyObject) {
let imagePicker = UIImagePickerController()
imagePicker.sourceType = .photoLibrary
imagePicker.mediaTypes = [kUTTypeImage as String, kUTTypeMovie as String]
imagePicker.delegate = self
self.present(imagePicker, animated: true, completion: nil)
}
func uploadImageToFirebaseStorage(data: NSData) {
let storageRef = FIRStorage.storage().reference(withPath: email/"/image.jpg")
let uploadMetadata = FIRStorageMetadata()
uploadMetadata.contentType = "image/jpeg"
let uploadTask = storageRef.put(data as Data, metadata: uploadMetadata) { (metadata, error) in
_ = metadata?.downloadURL
if (error != nil) {
print("I recieved an error! \(error?.localizedDescription)")
} else {
print ("Upload complete! Here's some metadata! \(metadata)")
}
let alert = UIAlertController(title: "Success!", message: "Image uploaded", preferredStyle: UIAlertControllerStyle.alert)
alert.addAction(UIAlertAction(title: "okay", style: UIAlertActionStyle.default, handler: nil))
self.present(alert, animated: true, completion: nil)
}
uploadTask.observe(.progress) { [weak self] (snapshot) in
guard let strongSelf = self else { return }
guard let progress = snapshot.progress else { return }
strongSelf.progressView.progress = Float(progress.fractionCompleted)
}
}
var toPass: String!
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
/*
// MARK: - Navigation
// In a storyboard-based application, you will often want to do a little preparation before navigation
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
// Get the new view controller using segue.destinationViewController.
// Pass the selected object to the new view controller.
}
*/
}
extension ThirdViewController: UIImagePickerControllerDelegate, UINavigationControllerDelegate {
func imagePickerControllerDidCancel(_ picker: UIImagePickerController) {
dismiss(animated: true, completion: nil)
}
func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
guard let mediaType: String = info[UIImagePickerControllerMediaType] as? String else {
dismiss(animated: true, completion: nil)
return
}
if mediaType == (kUTTypeImage as String) {
if let originalImage = info[UIImagePickerControllerOriginalImage] as? UIImage, let imageData = UIImageJPEGRepresentation(originalImage, 0.8) {
uploadImageToFirebaseStorage(data: imageData as NSData)
}
} else {
print("Please select an image")
}
dismiss(animated: true, completion: nil)
func prepareForSegue(segue: UIStoryboardSegue!, sender: AnyObject!) {
if (segue.identifier == "segueTest") {
//Checking identifier is crucial as there might be multiple
// segues attached to same view
if let fourthVC = segue.destination as? FourthViewController {
fourthVC.toPass = "email"
}
}
}
}
}