Throw an exception if article quality can't be determined
Throw an exception if article quality can't be determined

Currently, null will be implicitly returned which isn't supported by
callers.

Change-Id: I2a82019e436dc8b07c37cd6454e783431f6b6293

wikimedia/mediawiki-extensions-PageTriage,wikimedia/mediawiki-extensions-PageTriage,wikimedia/mediawiki-extensions-PageTriage