Cannot convert value of type '() -> _' to specified type 'NewsAPIResponse' - swift

Question

I thought my completionHandler returned a value of the type 'NewsAPIResponse', but I don't know how to assign it to a static var. Why is my code throwing an error? Is it not converting? I have checked all other areas of code for debugging. I am not sure whether the problem stems from how I created the completionHandler or not. Any insights would be greatly appreciated.
struct Article {
let site: String
let title: String
let date: Date
let tickers: String
let image: String
var siteText: String {
site
}
var titleText: String {
title
}
var tickerText: String {
tickers
}
var dateText: String {
"\(relativeDateFormatter.localizedString(for: date, relativeTo:Date()))"
}
var imageURL: URL? {
URL(string: image)
}
}
extension Article: Codable{}
extension Article: Identifiable{
var id: String{title}
}
struct NewsAPIResponse : Decodable{
let content: [Article]
}
extension Article {
func fetchData(completionHandler: #escaping (NewsAPIResponse) -> Void) {
let url = URL(string: "My API KEY")
var request = URLRequest(url: URL!)
request.addValue("application/json", forHTTPHeaderField: "Accept")
let task = URLSession.shared.dataTask(with: url!) { data, response, error in
guard error == nil else {
print(error!)
return
}
guard let data = data else {
print("Data is empty")
return
}
let jsonDecoder = JSONDecoder()
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
jsonDecoder.dateDecodingStrategy = .formatted(dateFormatter)
let apiResponse = try!jsonDecoder.decode(NewsAPIResponse.self, from: data)
completionHandler(apiResponse)
}
task.resume()
}
static var previewData: NewsAPIResponse = { //error is thrown here
let response = fetchData(){[weak self](apiResponse) in
}
return response
}
}