Call x-callback-url from OmniJS?

If I run this code in OmniOutliner iOS console,

(() => {
	'use strict';
	const 
		strURL = 'workflow://run-workflow?name=test&input=23';

	return URL.fromString(strURL).call(x =>
		console.log(x.toString())
	)
})();

It opens workflow app, and I get this output.

Collage_Fotor copy

I can successfully pass a number from OmniOutliner to Workflow and output it through OmniOutliner console. I cannot do the same with a string. I wonder why is that.