Sort rank 0 should not core dump.
unique=:({./.~)@:(/:~"_1)
unique'abc'
Process J segmentation fault (core dumped)
JVERSION
Engine: j804/j64/linux
Release: commercial/2015-12-28 10:47:03
Library: 8.04.15
Platform: Linux 64
Installer: unknown
InstallPath: /usr/share/j/8.0.4
Contact: www.jsoftware.com
/:~"0'abc' NB. sorting rank 0 core dumps
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