Firebase Database query not populating my array for tableview

Question

I think I have a strange one here.... I am getting an

fatal error: unexpectedly found nil while unwrapping an Optional value

when I am trying to get data from my Firebase database for my tableview. I used the code in another part of my app and it works great, so not sure why it is not working here...

I have built a data model:

import Foundation
import Firebase
import FirebaseDatabase

class Modules {

    private var _originalModules: String!
    private var _imageUrl: String!
    private var _postKey: String!
    private var _postRef: FIRDatabaseReference!


    var originalModules: String {
        return _originalModules
    }

    var imageUrl: String {
        return _imageUrl
    }

    var postKey: String {
        return _postKey
    }

    init(originalModules: String, imageUrl: String) {
        self._originalModules = originalModules
    //    self._imageUrl = caption
    }

    init(postKey: String, postData: Dictionary<String, AnyObject>) {
        self._postKey = postKey

        if let originalModules = postData["originalModules"] as? String {
            self._originalModules = originalModules

        }

        if let imageUrl = postData["imageUrl"] as? String {
            self._imageUrl = imageUrl


        _postRef = DataService.ds.REF_MODULE.child(_postKey)

        }
    }
}

I presume that I am connected to the database as I can print the correct data into the consul using this code:

DataService.ds.REF_MODULE.queryOrdered(byChild: "originalModules").observe(.value, with: { (snapshot) in

       self.modulesArray = []
if let snapshot = snapshot.children.allObjects as? [FIRDataSnapshot] {
                    for snap in snapshot {
                        print("SNAP: \(snap)")

then when I try to put this data into the array with the code below I cannot print into the consul and I receive the error mentioned above.

if let postDict = snap.value as? Dictionary<String, AnyObject>{
                        let key = snap.key as String
                        let post = Modules(postKey: key, postData: postDict)
                        self.modulesArray.insert(post, at: 0)
                        //self.modulesArray.append(post)
                        print ("This is the array from Firebase: \(self.modulesArray)")

The error also highlights the line with return _originalModules in the data model, so I presume that the array is empty because I have not properly linked the data call and the array somehow

Any and all help is greatly appreciated! Let me know if you require any clarification in order to provide me with solutions.

UPDATE! Database Structure

{
  "Module" : {
    "originalModules" : {
      "CreatingResults" : "Creating Results",
      "EffectiveCommunication" : "Effective Communication",
      "PresentationSkills" : "Presentation Skills",
      "ProblemSolving" : "Problem Solving",
      "SelfAwareness" : "Self Awareness",
      "Teamwork" : "Teamwork"
    }
  },
   "posts" : {
    "-KcTZfFT58IPT5ZJJRPX" : {
      "caption" : "hello?",
      "imageUrl" : "https://firebasestorage.googleapis.com",
      "likes" : 1
    },
    "-KcTZodrcehJ-VmSU0Lh" : {
      "caption" : "Erin is a nerd",
      "imageUrl" : "https://firebasestorage.googleapis.com",
      "likes" : 1
    },
}

and for what it is worth - the tableview code...

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

      let post = modulesArray[indexPath.row]

        let cell = tableView.dequeueReusableCell(withIdentifier: textCellIdentifier, for: indexPath) as! PerfectPracticeTableViewCell

        cell.configureCell(post: post)

        return cell
    }

and the configureCell code:

class PerfectPracticeTableViewCell: UITableViewCell {


    @IBOutlet weak var ppTableLabel: UILabel!
    @IBOutlet weak var ppTableImage: UIImageView!
    @IBOutlet weak var backgroundCardView: UIView!

    var modulesArray: Modules!



    func configureCell(post: Modules) {
        self.modulesArray = post
        self.ppTableLabel?.text = post.originalModules
      //  cell.ppTableImage?.image = image[(indexPath as NSIndexPath).row]
    }