             return self.httpHeaderFields
         }
 
-        var newHTTPHeaderFields = self.httpHeaderFields ?? [String: String]()
+        var newHTTPHeaderFields = self.httpHeaderFields ?? [:]
         unwrappedHeaders.forEach { key, value in
             newHTTPHeaderFields[key] = value
         }

            return self.parameters
        }

        var newParameters = self.parameters ?? [String: Any]()
        unwrappedParameters.forEach { key, value in
            newParameters[key] = value
        }

    public var urlRequest: URLRequest? {
        guard let requestURL = Foundation.URL(string: url) else { return nil }

        var request = URLRequest(url: requestURL)
        request.httpMethod = method.rawValue
        request.allHTTPHeaderFields = httpHeaderFields

