Missing migrations directory throws unhelpful NPE

[jpolchlo]

While working on another project, I ended up spending a long time chasing down a NullPointerException inside Drift. I found the culprit being that the configured migrations directory (as indicated by the :directory key in the config map) was missing. As a new user, the NPE was unhelpful, since I had inherited my code, which I had presumed ran correctly in the past. The NPE didn't provide useful breadcrumbs.

The location in question in Drift that raised the unhelpful NPE is here:

drift/src/drift/core.clj

Lines 114 to 119 in 1acfe11

	(defn default-migration-namespaces []
	(->> (find-migrate-directory)
	.listFiles
	(map #(.getName ^File %))
	(filter #(re-matches #".*\.clj$" %))
	(map namespace-string-for-file)))

I'd imagine that a null check that throws a useful missing directory error might help someone else in the future.