Merge branch 'master' of https://github.com/michalkop93/c3 into michalkop93-master
Merge pull request #1 from masayuki0812/master

merging upstream
fixes errors on null data

fixes errors thrown when provided with null array e.g.
['data',null,null]
Merge branch 'master' of https://github.com/michalkop93/c3 into michalkop93-master
Fix conflict