code: public void setAttribute(String attrname, String value) {
          if (attributes == null)
              attributes = new ArrayList<Attribute>();
          Attribute.setAttribute(attributes, attrname, value);
      }
docs: Set the value of a process attribute.
  If the value is null, the attribute is removed.
  If the attribute does not exist and the value is not null, the attribute
  is created.
  @param attrname
  @param value