_stringOrFunction = function (option, config, dt) {
	if (option === null || option === undefined) {
		return null;
	}
	else if (typeof option === 'function') {
		return option(config, dt);
	}
	return option;
}
Simply utility method to allow parameters to be given as a function

@param {undefined|string|function} option Option
@return {null|string} Resolved value