fix(api): empty dropdown data was overriden by previous data

Revert and proper fix of #2175
I forgot to check for an empty dropdown value. Jquery unfortunately does not return the field at all on serializeArray when multiple named fields (which should return an array) are empty.

Author: lubber-de

src/definitions/behaviors/api.js

@@ -74,6 +74,7 @@ $.api = $.fn.api = function(parameters) {
         url,
         data,
         requestStartTime,
+        originalData,
 
         // standard module
         element         = this,
@@ -86,6 +87,7 @@ $.api = $.fn.api = function(parameters) {
 
         initialize: function() {
           if(!methodInvoked) {
+            originalData = settings.data;
             module.bind.events();
           }
           module.instantiate();
@@ -197,7 +199,7 @@ $.api = $.fn.api = function(parameters) {
 
           // Add form content
           if(settings.serializeForm) {
-            settings.data = module.add.formData(settings.data);
+            settings.data = module.add.formData(originalData || settings.data);
           }
 
           // call beforesend and get any settings changes
@@ -428,7 +430,7 @@ $.api = $.fn.api = function(parameters) {
               formData = {},
               hasOtherData
             ;
-            data         = data || settings.data;
+            data         = data || originalData || settings.data;
             hasOtherData = $.isPlainObject(data);
 
             $.each($form.serializeArray(), function (i, element) {
@@ -443,9 +445,6 @@ $.api = $.fn.api = function(parameters) {
               } else {
                 formData[element.name] = element.value;
               }
-              if(hasOtherData && data[element.name]) {
-                delete data[element.name];
-              }
             });
 
             if(hasOtherData) {