title: how to fix GIT error: object file is empty when switching branch
body: <p>i am in the branch <code>master</code>. when checkout to <code>zc</code> branch , i was informed <code>object file is empty</code>.</p>
  
  <pre><code>$ git branch 
    demo
    develop
  * master
    zc
  
  $ git checkout zc
  error: unable to find 00d2a5741d54116a156e477093c3fcf30b24c6b3
  error: unable to read sha1 file of doc/build/html/_sources/props/buyhp.txt (00d2a5741d54116a156e477093c3fcf30b24c6b3)
  error: object file .git/objects/ee/4fc9118d213089e959b1625405c4b835cd4af7 is empty
  error: unable to find ee4fc9118d213089e959b1625405c4b835cd4af7
  error: object file .git/objects/ee/4fc9118d213089e959b1625405c4b835cd4af7 is empty
  fatal: loose object ee4fc9118d213089e959b1625405c4b835cd4af7 (stored in .git/objects/ee/4fc9118d213089e959b1625405c4b835cd4af7) is corrupt
  </code></pre>