@Override
 public Object eval() throws ExpressionException {
   try {
     return store.getValue(name);
   } catch (Exception e) {
     throw newExpressionException(e.getLocalizedMessage());
   }
 }
 @Override
 public void setStore(StateStore store) throws ExpressionException {
   this.store = store;
   try {
     store.getValue(name);
   } catch (Exception e) {
     throw newExpressionException(e.getLocalizedMessage());
   }
 }