invalidSelection error: cant't find the problem.

I have copied all of my code from VendingMachine.swift. I keep getting an invalidSelection error and I can not seem to figure out what is causing the issue.

import Foundation

enum VendingSelection: String { case soda case dietSoda case chips case cookie case sandwhich case wrap case candyBar case popTart case water case fruitJuice case sportsDrink case gum }

protocol VendingItem { var price: Double { get } var quantity: Int { get set } }

protocol VendingMachine { var selection: [VendingSelection] { get } var inventory: [VendingSelection: VendingItem] { get set } var amountDeposited: Double { get set }

init(inventory: [VendingSelection: VendingItem])
func vend(_ quantity: Int, _ selection: VendingSelection) throws
func deposit(_ amount: Double)

}

struct Item: VendingItem { let price: Double var quantity: Int }

enum InventoryError: Error { case invalidResource case conversionFailure case invalidSelection }

class PlistConverter { static func dictionary(fromFile name: String, ofType type: String) throws -> [String: AnyObject] { guard let path = Bundle.main.path(forResource: name, ofType: type) else { throw InventoryError.invalidResource }

    guard let dictionary = NSDictionary(contentsOfFile: path) as? [String: AnyObject] else {
        throw InventoryError.conversionFailure
    }

    return dictionary
}

}

class InventoryUnarchiver {

static func vendingInventory(fromDictionary dictionary: [String: AnyObject]) throws -> [VendingSelection: VendingItem] {

    var inventory: [VendingSelection:VendingItem] = [:]

    for (key, value) in dictionary{
        if let itemDictionary = value as? [String: Any], let price = itemDictionary["price"] as? Double, let quantity = itemDictionary["quantity"] as? Int{
            let item = Item(price : price, quantity : quantity)

            guard let selection = VendingSelection(rawValue: key) else{
                throw InventoryError.invalidSelection
            }

            inventory.updateValue(item, forKey: selection)
        }
    }

    return inventory
}

} class FoodVendingMachine: VendingMachine {
let selection: [VendingSelection] = [.soda, .dietSoda, .cookie, .sandwhich, .candyBar, .popTart, .water, .fruitJuice, .sportsDrink, .gum]

var inventory: [VendingSelection : VendingItem]
var amountDeposited: Double = 10.00

required init(inventory: [VendingSelection : VendingItem]) {
    self.inventory = inventory
}

func vend(_ quantity: Int, _ selection: VendingSelection) throws {

}

func deposit(_ amount: Double) {

}

}