I think this isn't a well-worded changelog entry.  The fact that we are using the accessor is an implementation detail.  Instead, how about:

> Fix `NoMethodError` that was being raised when the shared example group registry was cleared before there were any shared example groups (thepoho, Jon Rowe).

The difference is that this describes the externally visible bug that was fixed rather than the implementation of the fix.  We should alway strive to write our changlog entries such that they describe changes in a way that's meaningful to end users (who may know very little about how RSpec is implemented).