Error handling using guard statement compiles but does not throw correct error!

I'm trying to implement error handling using a guard statement as described by the Instructor.

Here is the problem assigned: Challenge Task 1 of 3

In the editor, you have a struct named Parser whose job is to deconstruct information from the web. The incoming data can be nil, keys may not exist, and values might be nil as well. In this task, complete the body of the parse function. If the data is nil, throw the EmptyDictionary error. If the key "someKey" doesn't exist throw the InvalidKey error. Hint: To get a list of keys in a dictionary you can use the keys property which returns an array. Use the contains method on it to check if the value exists in the array

If you take a look at my code i'm throwing the right error. However, the automatic grading response "is that I need to throw the InvalidKey error which is what I'm throwing, so I'm unclear as to why this is the case.

below is my code.

enum ParserError: ErrorType {
  case EmptyDictionary
  case InvalidKey
}

struct Parser {
  var data: [String : String?]?

  func parse() throws {
   guard let notEmpty = data?.keys else {
    throw ParserError.EmptyDictionary
    }
   guard let hasKey = data?.keys.contains("someKey") else {
    throw ParserError.InvalidKey
    }
  }
}

let data: [String : String?]? = ["someKey": nil]
let parser = Parser(data: data)