Got "Unknown type, this should not get triggered"

[antononcube]

Using the package's example file "antlr2perl6" over the file InputFormLexerRules.g4, I got the following error:

Unknown type, this should not get triggred
  in method to-lines at /Applications/Rakudo/share/perl6/site/sources/04CF9BA541DE71DF8E77833BA483DE2123FD57EC (ANTLR4::Grammar) line 63
  in method file-to-string at /Applications/Rakudo/share/perl6/site/sources/04CF9BA541DE71DF8E77833BA483DE2123FD57EC (ANTLR4::Grammar) line 226
  in sub MAIN at ./antlr2perl6 line 6
  in block <unit> at ./antlr2perl6 line 2

I just comment out in InputFormLexerRules.g4 the lines:

options{
  //We put target-language dependent code in a base class.
  superClass=LexerBase;
}

and I was able to proceed.

(For more details see https://github.com/antononcube/Raku-Mathematica-Grammar .)