code: public int doEndTag()
              throws JspException {
  
          if(hasErrors())
              reportErrors();
          else {
              AbstractCallMethod cm = (AbstractCallMethod)getParent();
              cm.addParameter(_type, _isNull ? null : _value);
          }
  
          localRelease();
          return EVAL_PAGE;
      }
docs: Prepare the value to pass up to the {@link AbstractCallMethod} type
  parent.
  
  @return {@link #EVAL_PAGE} to continue evaluating the page