First day for bicycle

Today is sunny,  this is first time i  use bicycle  Substitute  bus go to work.Breeze was blowing, i feel so good.So  it's the first blog  here

today when i set up envirment,  as the code is begin update , so  there is a bug, after  three hours , i confirm that this is a bug.

just because for  null object. when a  ref  object is deleted,  the just is not  think over  null, so bug is generate.