Issues while validating snapcraft.yaml: None is not of type 'string'

I have an example project based on the code snippet in the document of "
Snappy Ubuntu Core - Application Developer Manual 15.04". My project is located at:

https://github.com/liu-xiao-guo/null

snapcraft.yaml

parts:
  example-part:
    plugin: null
    stage-packages:
      - gpg
      - wget
    organize:
      opt/bin: bin
    filesets:
      binaries:
       - bin/*
       - usr/bin/*
      headers:
       - *.h
       - -include
    stage:
      - $binaries
      - test/bin/test_app
      - $headers
    snap:
      - $binaries

There are a few bugs related to the project:

1) - *.h gives me the following error:
Issues while validating snapcraft.yaml: expected alphabetic or numeric character, but found '.' on line 20 of snapcraft.yaml

2) If I take out the above line, I come out the following error:
Issues while validating snapcraft.yaml: None is not of type 'string'

3) By the way, I do not fully understand what the "oganize" mean in such a context. the explanation in the document is very weak.

I do not have any clue about the error. By the way, I have changed the "type" in the document to "plugin". However, the errors are the same.

Thanks & best regards,
XiaoGuo