Human task form parameter

Question

hi,
how I can copy value of parameters in one form to another form ,Imaging I have 2 human task ,I want when the first human task has executed ,I could copy the value of its parameters to second humantasks' form.
I have done below steps in assign activity :
in from secetion: /task:task/task:payload/task:family //family is a parameter in first form
in to section: name //that name is a global variable.
but in run time I have this error :
<selectionFailure xmlns="http://schemas.xmlsoap.org/ws/2003/03/business-process/"><part name="summary"><summary>empty variable/expression result.
xpath variable/expression expression "/task:task/task:payload/task:family" is empty at line 190, when attempting reading/copying it.
Please make sure the variable/expression result "/task:task/task:payload/task:family" is not empty.
</summary>
</part></selectionFailure>
what is the problem?what I should do?
best regards

Answer 1

Well it looks like in your task form you don't fill in a value for the family-element, so after the form is completed you assign on an empty-element, which results in this.
Can't you copy the whole payload-element instead of every subelement itself?
Or instead of the assign use a transformation between the outputvariable of form1 to the inputvariable of form2. If fields are left empty , the transformation won't fail, and the target element in form2 is just empty.