Skip output check if output not defined on formatter
Created by: niceking
If a custom formatter doesn't subclass the BaseTextFormatter
it doesn't have the output
method, then the duplicate formatter check throws a "undefined method output" error, just PR just skips that part of the check if the output
method isn't defined.
Also I've noticed in the documentation for custom formatters that the text recommends subclassing from BaseTextFormatter
but the example doesn't show that? I totally just read the code and skimmed the text