resolves #1869

Fixes:

• refactor check of all falsy condition of plugins and opts before returing NoWorkResult in Processor.process().

postcss/lib/processor.js

Lines 44 to 55 in a0a82d3

	process(css, opts = {}) {
	if (
	this.plugins.length === 0 &&
	typeof opts.parser === 'undefined' &&
	typeof opts.stringifier === 'undefined' &&
	typeof opts.syntax === 'undefined'
	) {
	return new NoWorkResult(this, css, opts)
	} else {
	return new LazyResult(this, css, opts)
	}
	}

For a full repro see : https://github.com/romainmenke/postcss-no-work-result-sourcemaps

By setting parser: null as a processing option you can force a LazyResult.

Setting null instead of undefined is a common mistake, especially when not using TypeScript.

Is it intentional that NoWorkResult and LazyResult have different CSS outputs?