Fix #179: Can't send empty string with utf8 serializer

www/helpers.js

@@ -213,8 +213,6 @@ function getAllowedDataTypes(dataSerializer) {
 }
 
 function getProcessedData(data, dataSerializer) {
-  data = data || {};
-
   var currentDataType = getTypeOf(data);
   var allowedDataTypes = getAllowedDataTypes(dataSerializer);
 
@@ -248,7 +246,7 @@ function handleMissingOptions(options, globals) {
     timeout: checkTimeoutValue(options.timeout || globals.timeout),
     headers: checkHeadersObject(options.headers || {}),
     params: checkParamsObject(options.params || {}),
-    data: options.data || null,
+    data: getTypeOf(options.data) === 'Undefined' ? null : options.data,
     filePath: options.filePath || '',
     name: options.name || ''
   };