Fix error when a field is null and flatten is used

[juanjoDiaz]

Closes #273

[coveralls]

Coverage remained the same at 100.0% when pulling d4ae494 on juanjoDiaz:fix_null_error_on_flatten into e3ebed6 on zemirco:master.

[juanjoDiaz]

What the hell?!?! It seems that the table library decided to include colors in some older node? That's weird...

I'll have to check it.

Help is welcome :)

[juanjoDiaz]

Ok, so it's nothing to do with the code. Master also fails now: https://travis-ci.org/zemirco/json2csv/jobs/359058666

Has anything changed in Travis @knownasilya ?

[knownasilya]

Not that I'm aware of, maybe they updated the images..

[juanjoDiaz]

I removed all the colors introduced by table-cli2 (which are the tests failing) but the error persists.
So I'm totally clueless about what's including the colors all the sudden.

I had spent 2 weeks researching this and have no answer. Since master is already failing and this PR definitely work and is 100% unrelated to the failing tests, I'd suggest that we merge this and I'll create a new issue for the failing tests. 😞