Although this is accurate, it is probably not much use to the developer as they don't necessarily understand that this exception is being thrown in a helper function. It might be helpful to explain that AngularJS often asserts that certain values must be present or truthy using this helper function, which throws if they are not.

(BTW, It seems that it is only ever used in the compiler to check that either a `scope` exists or that a `directiveFactory` exists. So perhaps this document should at least enumerate these two instances?)