sha,message,author_date,committer_date,raw_author,raw_committer,repo,author,committer
57ebf7df62461abbd6b6f5d45a79dda38e6ba001,"Change np.isnan to pd.isnull in conventions.py to handle _FillValue = ''

At a number of spots in conventions.py, np.isnan was being used
to check possible fill values.  However, np.isnan is not implemented
for string types.  So, I've replaced np.isnan with pd.isnull.

Alas, I haven't been able to update the tests to cover _FillValue = '',
because doing so would involve significant changes throughout the
code base.",2014-06-01T23:41:57Z,2014-06-15T23:08:00Z,104374218f09fa09e00ed69a5a87e55565c8d67f,104374218f09fa09e00ed69a5a87e55565c8d67f,13221727,,