<p> This class implements the <code>Serializable</code> interface, but does
  not define a <code>serialVersionUID</code> field.&nbsp;
  A change as simple as adding a reference to a .class object
    will add synthetic fields to the class,
   which will unfortunately change the implicit
   serialVersionUID (e.g., adding a reference to <code>String.class</code>
   will generate a static field <code>class$java$lang$String</code>).
   Also, different source code to bytecode compilers may use different
   naming conventions for synthetic variables generated for
   references to class objects or inner classes.
   To ensure interoperability of Serializable across versions,
   consider adding an explicit serialVersionUID.</p>