Error: from config: failed to resolve output format "print" from site config

[domingosbarreto]

When working on the website content, without changing any value on config, started giving the following error when running hugo server:

Error: from config: failed to resolve output format "print" from site config

Already tried with a new site and I get the same error.

With an empty hugo site or other theme the error does not occurs.

[LisaFC]

Duplicate of #805 - try some of the suggestions there and I'll follow up in that issue if they don't work.