     }
     
     private func initializeMultipartRequest(request: NSMutableURLRequest, boundary: String) {
-        request.addValue("multipart/form-data; boundary=\(boundary)", forHTTPHeaderField: "Content-Type")
+        request.setValue("multipart/form-data; boundary=\(boundary)", forHTTPHeaderField: "Content-Type")
     }
     
     private func appendStringToMultipartData(data: NSMutableData, boundary: String, name: String, value: String) {

    
    // MARK: - Parameter types
    
    struct FileParameter: RequestMultipartFormDataParameter {
        let name: String
        let filename: String
        let contentType: String
        let data: NSData
    }
    
    struct StringParameter: RequestMultipartFormDataParameter {
        let name: String
        let value: String
    }
    
}


public class RequestMultipartFormDataParameters: RequestParameters {
    
    public let parameters: [RequestMultipartFormDataParameter]
    
    public init(_ parameters: [RequestMultipartFormDataParameter]) {
        self.parameters = parameters
    }
    
