Directive resolver problem

Hi guys.
I want to use my own directive “isAuthenticated” for some fields and mutations.
User object or null is in context.user.
And I’m trying to do smth like this:

    isAuthenticated: (next, source, args, context) => {
	 if (context.user) {
		return next()
	 } else {
		throw new Error(`Must be logged in to view this field`)


And it works fine in GraphiQL: data object, error object, server got error, looks like OK.

But my React app completely crashes.

What have to be in else-block???