FYI, I don't see SET SQLBLANKLINES documented in the v12 manual.
I hope it just never made it into the docs, as opposed to having been DE-supported at some point in the last 8 years...? (I haven't tested it yet.)
I've read through the Command Window chapter of the manual quite a bit lately, and would have never known this command exists (not a SQL*Plus expert) except that I happened to spot it being used in someone's example script in a recent forum post, which prompted me to look it up.
We've had deployments fail recently because of blank lines in scripts, and this should really help us.