Build fails with Crystal 1.7.2

[binarytemple]

~/repos/bt/EBNF.cr/ asdf which crystal                  /Users/b/.asdf/installs/crystal/1.7.2/bin/crystal

~/repos/bt/EBNF.cr/ asdf which shards 
/Users/b/.asdf/installs/crystal/1.7.2/embedded/bin/shards

~/repos/bt/EBNF.cr/ shards build --release --production
Dependencies are satisfied
Building: ebnf
Error target ebnf failed to compile:
Showing last frame. Use --error-trace for full trace.

In src/ebnf/grammar/rule.cr:89:48

 89 | def initialize(@atoms = Array(Atom).new, @action = nil)
                                               ^
Error: instance variable @action of EBNF::Bison::Rule was inferred to be Nil, but Nil alone provides no information

[binarytemple]

It worked with Crystal 0.33.
I'm trying to get it to parse the Postgres Bison Grammar - https://github.com/postgres/postgres/blob/master/src/backend/parser/gram.y
My goal is to automate the conversion of the postgres grammar into a intermediate format from whence I can create an (Erlang) Yecc grammar.
Any general advice welcomed as well, maybe I'm taking the wrong approach.