Reading a non-existent property on an object always returns ``++undefined++``. Doing so is usually an error; either in the name of the property or the type of the variable being accessed.
If an attempt is made to access properties of a primitive, the primitive is automatically encased in a primitive-wrapper object for the operation. But being "promoted" to an object doesn't mean that the primitive will actually have properties to access. The wrapper object still won't have the non-existent property and ``++undefined++`` will be returned instead.
This rule raises an issue when an attempt is made to access properties of a primitive. Thus this rule should only be activated when you don't use monkey patching for standard objects, like ``++Number++``, ``++Boolean++`` and ``++String++``.
The Ember framework introduces a few extensions to ``++String++``. Since it is a widely used package, the following ``++String++`` properties will not trigger this rule even though they are not built-in:
