In cljs.core/pr-sequential-writer, there is a loop that initializes n to be the result of dec, and upon recur, dec is also caused to form the next value of n.
In the scope of that loop there is an expression
which can be simplified to
because n is known to be a number, and cannot be nil.
Nil check removed.
CLJS-3081-0.patch passes CI
CLJS-3081-0.patch passes Canary
CLJS-3081-0.patch added to Patch Tender