                         format: format,
                         options: options
                 )
-                mutableURLRequest.setValue("application/x-plist", forHTTPHeaderField: "Content-Type")
+
+                if mutableURLRequest.valueForHTTPHeaderField("Content-Type") == nil {
+                    mutableURLRequest.setValue("application/x-plist", forHTTPHeaderField: "Content-Type")
+                }
+
                 mutableURLRequest.HTTPBody = data
             } catch {
                 encodingError = error as NSError

                let options = NSJSONWritingOptions()
                let data = try NSJSONSerialization.dataWithJSONObject(parameters, options: options)

                mutableURLRequest.setValue("application/json", forHTTPHeaderField: "Content-Type")
                mutableURLRequest.HTTPBody = data
            } catch {
                encodingError = error as NSError

            while index != string.endIndex {
                let startIndex = index
                let endIndex = index.advancedBy(batchSize, limit: string.endIndex)
                let range = startIndex ..< endIndex

                let substring = string.substringWithRange(range)

