Parse query string from NSURL

NSURL_Extensions.swift

// Example:
let url = NSURL(string: "https://example.com/hello?bla=one&bla=two&foo&bar=1")!
let values = url.parseQueryString()
// Result: ["bla": ["one", "two"], "bar": ["1"], "foo": []]

extension NSURL {
    func parseQueryString() -> [String: [String]]? {
        guard let items = NSURLComponents(URL: self, resolvingAgainstBaseURL: false)?.queryItems else {
            return nil
        }
        var data = [String: [String]]()
        for item in items {
            var list = data[item.name] ?? [String]()
            if let value = item.value {
                list.append(value)
            }
            data[item.name] = list
        }
        return data
    }
}