     }
     
     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) {


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

    
    // MARK: - Parameter types
    
   public struct FileParameter: RequestMultipartFormDataParameter {
        public let name: String
        public let filename: String
        public let contentType: String
        public let data: NSData
    
        public init(name: String, filename: String, contentType: String, data: NSData) {
            self.name = name
            self.filename = filename
            self.contentType = contentType
            self.data = data
        }
    }
    
    public struct StringParameter: RequestMultipartFormDataParameter {
        public let name: String
        public let value: String
        
        public init(name: String, value: String) {
            self.name = name
            self.value = value
        }
    }
    
}
