The wcminit component is used only on the author to initialize the authoring ui, either classic or touch. This component is only rendered, when the wcmmode is not disabled. However even in this case sightly tries to initialize the WcmInit controller, which has an injection of AuthoringUIMode object. In disabled mode this object is null and therefore following exception occurs:
fixed in sling models extension - defaults to TOUCH if mode is not set, otherwise it would be too easy to forget the @optional annotation when injecting this mode.