Fixed issue #944 - Remove all Users from Overview does not work.

app/assets/javascripts/app/controllers/_application_controller_form.coffee

@@ -426,8 +426,11 @@ class App.ControllerForm extends App.Controller
         delete param[item.name]
         continue
 
-      # collect all params, push it to an array if already exists
-      value = item.value.trim()
+      # collect all params, push it to an array item.value already exists
+      value = item.value
+      if item.value
+        value = item.value.trim()
+
       if item.type is 'boolean'
         if value is ''
           value = undefined

app/assets/javascripts/application.js

@@ -246,13 +246,27 @@ jQuery.fn.extend( {
       var val = $elem.val();
       var type = $elem.data('field-type');
 
-      return val == null ?
-        null :
-        jQuery.isArray( val ) ?
-          jQuery.map( val, function( val ) {
-            return { name: elem.name, value: val.replace( rCRLF, "\r\n" ), type: type };
-          } ) :
-          { name: elem.name, value: val.replace( rCRLF, "\r\n" ), type: type };
+      var result;
+      if ( val == null ) {
+
+        // be sure that also null values are transfered
+        // https://github.com/zammad/zammad/issues/944
+        if ( $elem.prop('multiple') ) {
+          result = { name: elem.name, value: null, type: type };
+        }
+        else {
+          result = null
+        }
+      }
+      else if ( jQuery.isArray( val ) ) {
+        result = jQuery.map( val, function( val ) {
+          return { name: elem.name, value: val.replace( rCRLF, "\r\n" ), type: type };
+        } );
+      }
+      else {
+        result = { name: elem.name, value: val.replace( rCRLF, "\r\n" ), type: type };
+      }
+      return result;
     } ).get();
   }
 } );

public/assets/tests/form_column_select.js

@@ -28,6 +28,7 @@ test( "column_select check", function(assert) {
 
   var params = App.ControllerForm.params(el)
   var test_params = {
+    column_select1: null,
     column_select2: ['aaa', 'bbb'],
     column_select3: ['1', '2'],
   }