library usage

[Dimid Duchovny <dimidd@gmail.com>]

Hello,

I've tried to use the library with a simple example, 2 messages where
one is a reply to the other:
require 'msgthr'
m1 = {id: 1, subject: 's1'}
m2 = {id: 2, subject: 're: s1'}
msgthr = Msgthr.new
msgthr.add 1, nil, m1
msgthr.add 2, [1], m2
msgthr.thread!
msgthr.walk_thread do |level, container, index|
  msg = container.msg
  subject = msg ? msg[:subject] : "[missing: <#{container.mid}>]"
  indent = '  ' * level
  printf("#{indent} % 3d. %s\n", index, subject)
end

Which fails with:
msgthr.rb:9:in `block in <main>': undefined method `msg' for
#<Array:0x00007ff404841958> (NoMethodError)

Am I missing something?