如果atom编辑器下使用platformio时出现build错误如下：（/home/ft是我的用户目录，根据你的用户名而不同）
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File "/home/ft/.platformio/penv/local/lib/python2.7/site-packages/platformio/commands/run.py", line 400, in check_project_envs
    unknown = set(environments) - known
TypeError: 'NoneType' object is not iterable

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An unexpected error occurred. Further steps:
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可以通过修改上面错误提示里'run.py'文件，修正这个错误. 定位到'run.py'文件400行，然后根据下面的说明修改代码：

400行->  unknown = set(environments) - known
把上面这行用下面的代码替换为：
    if environments:
        unknown = set(environments) - known
    else:
        unknown = set()
        click.secho('environments is None')
    # unknown = set(environments) - known