[perl #109674] [BUG] /<[]>/, the empty character class, should be synonymous with // but instead fails at parse time in Rakudo

[Christian Bartolomaeus via RT]

This seems to work now (<[]> behaves like <!>):

$ perl6 -e 'say so "a" ~~ /<[]>/'
False

$ perl6 -e 'say so "abc" ~~ /a <[]>/'
False

$ perl6 -e 'say so "" ~~ /<[]>/'
False

I added two tests to S05-mass/stdrules.t with commit 
https://github.com/perl6/roast/commit/9bad4dd1af

I'm closing this ticket now.