code: function callback(err,other) {
  			// check if the 'err' is boolean, if so then this is a 'exists' callback special case
  			if (err && (typeof err !== 'boolean')) return reject(err);
  			// convert arguments to proper array, ignoring error argument
  			let args = Array.prototype.slice.call(arguments, 1);
  			// if arguments length is one or more resolve arguments as array,
  			// otherwise resolve the argument as is.
  			return resolve(args.length < 2 ? args[0] : args);
  		}
docs: promisified callback