Error in ./src/cltk/lexers/ebnf.cr:28: instantiating 'Regex:Class#new(String, Regex::Options)'
   rule(/\*/) { :STAR     }
        ^
instantiating 'Regex#initialize(String, Regex::Options)'
in /opt/crystal/src/regex/regex.cr:224: instantiating 'String#gsub(Char, String)'
    source = source.gsub('\u{0}', "\\0")
                    ^~~~
in /opt/crystal/src/string.cr:1153: instantiating 'includes?(Char)'
    if includes?(char)
       ^~~~~~~~~
in /opt/crystal/src/string.cr:1715: instantiating 'index(Char)'
    !!index(search)
      ^~~~~
instantiating 'index(Char, Int32)'
in /opt/crystal/src/string.cr:1589: instantiating 'each_char_with_index()'
    each_char_with_index do |char, i|
    ^~~~~~~~~~~~~~~~~~~~
in /opt/crystal/src/string.cr:2327: instantiating 'each_char()'
    each_char do |char|
    ^~~~~~~~~
in /opt/crystal/src/string.cr:2298: instantiating 'Char::Reader:Class#new(String)'
      Char::Reader.new(self).each do |char|
                   ^~~
instantiating 'Char::Reader#initialize(String)'
in /opt/crystal/src/char/reader.cr:27: instantiating 'decode_current_char()'

      decode_current_char
      ^~~~~~~~~~~~~~~~~~~

in /opt/crystal/src/char/reader.cr:133: instantiating 'decode_char_at(Int32)'

      decode_char_at(@pos) do |code_point, width|
      ^~~~~~~~~~~~~~

in /opt/crystal/src/char/reader.cr:83: instantiating 'invalid_byte_sequence()'

        invalid_byte_sequence
        ^~~~~~~~~~~~~~~~~~~~~

in /opt/crystal/src/char/reader.cr:129: instantiating 'InvalidByteSequenceError:Class#new()'

      raise InvalidByteSequenceError.new
                                     ^~~

instantiating 'new(String)'

instantiating 'InvalidByteSequenceError#initialize(String)'

in /opt/crystal/src/exception.cr:165: instantiating 'super(String)'

    super(message)
    ^~~~~

in /opt/crystal/src/exception.cr:97: undefined method 'printable_backtrace' for Nil (compile-time type is (Nil | CallStack))

    @callstack.printable_backtrace
               ^~~~~~~~~~~~~~~~~~~

================================================================================

Error: instance variable '@callstack' of KeyError was not initialized in all of the 'initialize' methods, rendering '@callstack' of InvalidByteSequenceError nilable (Exception is the common supertype that defines it)

Specifically in these ones: