Steps to reproduce:

1. Create a ZUL markup with button and its onClick attribute. For simplicity, let's there'll be a simple arithmetic expression:

         <button label="Add Group" sclass="add-group-button"
                 onClick="@command('showGroupsDialog', mode='${10+1}')" />

   And the appropriate class:

2. Create a respective method in the ViewModel:

       @Command
       public void showGroupsDialog(@Param("mode") String mode) {
           Window branchDialog = (Window) getComponent("branchPermissionManagementWindow")

   Expected result: the mode parameter in the ViewModel should have value 11
   Actual result: the mode parameter has ${10+1} as its value.