perltidy does not know about //=

gistfile1.pl

#!/bin/perl
# Before perltidy
helper ndb => sub { state $db //= BCV::DB->new('SwitchCLLI') };
helper cdb => sub { state $db //= BCV::DB->new('STARS') };

# After perltidy
helper ndb => sub { state $db // = BCV::DB->new('SwitchCLLI') };
helper cdb => sub { state $db // = BCV::DB->new('STARS') };