[Feature Request] `format` should accept undefined as a valid value

Describe the bug

I want to add a custom formatter, but only in production mode. What I tried is this:

format: process.env.environment !== `production` ? undefined : ctx => `...`,

This works in production mode, but not in any other mode, because undefined isn’t a function.

TypeError: config.format is not a function   
    at Object.exports.formatMessage (...\node_modules\better-logging\dist\lib\formatMessage.js:44:37)     
    at ...\node_modules\better-logging\dist\lib\decorateObject.js:21:58

I’m guessing this is due to the use of something like Object.entries(), which will yield the key format with value undefined if format is specified as such, instead of omitting it, like it does when it’s actually not defined.

Expected behavior

A simple error handling to check if the value of format (or any other option, for that matter) is undefined, and if it is, handle it the exact same way as if it we actually undefined 😃

Desktop (please complete the following information):

• Windows 10, Node.js 14.15.1

Additional context

The package is great! 😄

[Olian04]

Implemented in release 4.5.0

[Olian04]

@Chaphasilor I think I’ve decided that I don’t have any strong opinions either way. So might as well go with your idea. I’ll have a look at a clean implementation soon.