Problem with precompilation / compile time / RakuAST

A.rakumod

# store this as lib/A.rakumod
use v6.*;

class A {

    my sub bar($a,$b) { "$a:$b" }

    method foo() {
        RakuAST::Sub.new(
          name => RakuAST::Name.from-identifier("b"),
          body => RakuAST::Blockoid.new(
            RakuAST::StatementList.new(
              RakuAST::Statement::Expression.new(
                expression => RakuAST::Call::Name.new(
                  name => RakuAST::Name.from-identifier("bar"),
                  args => RakuAST::ArgList.new(
                    RakuAST::IntLiteral.new(42),
                    RakuAST::IntLiteral.new(666)
                  )
                )
              )
            )
          )
        ).EVAL
    }
}

#my constant $foo = A.foo;  # fails
my $foo = A.foo;  # works
say $foo()

gistfile1.txt

$ raku -Ilib -MA --ll-exception -e ''  
chars requires a concrete string, but got null
   at NQP::src/vm/moar/QAST/QASTCompilerMAST.nqp:920  (/Users/liz/Github/rakudo/install/share/nqp/lib/QAST.moarvm:serialize_sc)
 from NQP::src/vm/moar/QAST/QASTCompilerMAST.nqp:925  (/Users/liz/Github/rakudo/install/share/nqp/lib/QAST.moarvm:deserialization_code)
 from NQP::src/vm/moar/QAST/QASTCompilerMAST.nqp:866  (/Users/liz/Github/rakudo/install/share/nqp/lib/QAST.moarvm:compile_node)
 from NQP::src/vm/moar/QAST/QASTCompilerMAST.nqp:700  (/Users/liz/Github/rakudo/install/share/nqp/lib/QAST.moarvm:as_mast)
 from NQP::src/vm/moar/QAST/QASTCompilerMAST.nqp:420  (/Users/liz/Github/rakudo/install/share/nqp/lib/QAST.moarvm:to_mast)
 from NQP::src/vm/moar/QAST/QASTCompilerMAST.nqp:2217  (/Users/liz/Github/rakudo/install/share/nqp/lib/QAST.moarvm:to_mast)
 from NQP::src/vm/moar/HLL/Backend.nqp:794  (/Users/liz/Github/rakudo/install/share/nqp/lib/NQPHLL.moarvm:mast)
 from NQP::src/HLL/Compiler.nqp:462  (/Users/liz/Github/rakudo/install/share/nqp/lib/NQPHLL.moarvm:execute_stage)
 from NQP::src/HLL/Compiler.nqp:501  (/Users/liz/Github/rakudo/install/share/nqp/lib/NQPHLL.moarvm:run)
 from NQP::src/HLL/Compiler.nqp:504  (/Users/liz/Github/rakudo/install/share/nqp/lib/NQPHLL.moarvm:)
 from NQP::src/HLL/Compiler.nqp:496  (/Users/liz/Github/rakudo/install/share/nqp/lib/NQPHLL.moarvm:compile)
 from NQP::src/HLL/Compiler.nqp:166  (/Users/liz/Github/rakudo/install/share/nqp/lib/NQPHLL.moarvm:eval)
 from NQP::src/HLL/Compiler.nqp:441  (/Users/liz/Github/rakudo/install/share/nqp/lib/NQPHLL.moarvm:evalfiles)
 from NQP::src/HLL/Compiler.nqp:364  (/Users/liz/Github/rakudo/install/share/nqp/lib/NQPHLL.moarvm:command_eval)
 from src/Perl6/Compiler.nqp:233  (/Users/liz/Github/rakudo/install/share/perl6/lib/Perl6/Compiler.moarvm:command_eval)
 from NQP::src/HLL/Compiler.nqp:289  (/Users/liz/Github/rakudo/install/share/nqp/lib/NQPHLL.moarvm:command_line)
 from src/main.nqp:81  (/Users/liz/Github/rakudo/install/share/perl6/runtime/perl6.moarvm:MAIN)
 from src/main.nqp:63  (/Users/liz/Github/rakudo/install/share/perl6/runtime/perl6.moarvm:<mainline>)
 from <unknown>:1  (/Users/liz/Github/rakudo/install/share/perl6/runtime/perl6.moarvm:<main>)
 from <unknown>:1  (/Users/liz/Github/rakudo/install/share/perl6/runtime/perl6.moarvm:<entry>)

   at SETTING::src/core.c/Exception.pm6:65  (/Users/liz/Github/rakudo/install/share/perl6/runtime/CORE.c.setting.moarvm:throw)
 from SETTING::src/core.c/control.pm6:255  (/Users/liz/Github/rakudo/install/share/perl6/runtime/CORE.c.setting.moarvm:die)
 from SETTING::src/core.c/CompUnit/PrecompilationRepository.pm6:461  (/Users/liz/Github/rakudo/install/share/perl6/runtime/CORE.c.setting.moarvm:precompile)
 from SETTING::src/core.c/CompUnit/PrecompilationRepository.pm6:55  (/Users/liz/Github/rakudo/install/share/perl6/runtime/CORE.c.setting.moarvm:try-load)
 from SETTING::src/core.c/CompUnit/Repository/FileSystem.pm6:116  (/Users/liz/Github/rakudo/install/share/perl6/runtime/CORE.c.setting.moarvm:)
 from SETTING::src/core.c/CompUnit/Repository/FileSystem.pm6:110  (/Users/liz/Github/rakudo/install/share/perl6/runtime/CORE.c.setting.moarvm:need)
 from src/Perl6/World.nqp:1501  (/Users/liz/Github/rakudo/install/share/perl6/lib/Perl6/World.moarvm:load_module)
 from src/Perl6/World.nqp:1439  (/Users/liz/Github/rakudo/install/share/perl6/lib/Perl6/World.moarvm:do_pragma_or_load_module)
 from src/Perl6/World.nqp:816  (/Users/liz/Github/rakudo/install/share/perl6/lib/Perl6/World.moarvm:comp_unit_stage1)
 from src/Perl6/Grammar.nqp:839  (/Users/liz/Github/rakudo/install/share/perl6/lib/Perl6/Grammar.moarvm:comp_unit)
 from src/Perl6/Grammar.nqp:554  (/Users/liz/Github/rakudo/install/share/perl6/lib/Perl6/Grammar.moarvm:TOP)
 from NQP::src/QRegex/Cursor.nqp:1224  (/Users/liz/Github/rakudo/install/share/nqp/lib/QRegex.moarvm:parse)
 from NQP::src/HLL/Compiler.nqp:553  (/Users/liz/Github/rakudo/install/share/nqp/lib/NQPHLL.moarvm:parse)
 from NQP::src/HLL/Compiler.nqp:465  (/Users/liz/Github/rakudo/install/share/nqp/lib/NQPHLL.moarvm:execute_stage)
 from NQP::src/HLL/Compiler.nqp:501  (/Users/liz/Github/rakudo/install/share/nqp/lib/NQPHLL.moarvm:run)
 from NQP::src/HLL/Compiler.nqp:504  (/Users/liz/Github/rakudo/install/share/nqp/lib/NQPHLL.moarvm:)
 from NQP::src/HLL/Compiler.nqp:496  (/Users/liz/Github/rakudo/install/share/nqp/lib/NQPHLL.moarvm:compile)
 from NQP::src/HLL/Compiler.nqp:166  (/Users/liz/Github/rakudo/install/share/nqp/lib/NQPHLL.moarvm:eval)
 from NQP::src/HLL/Compiler.nqp:309  (/Users/liz/Github/rakudo/install/share/nqp/lib/NQPHLL.moarvm:)
 from NQP::src/HLL/Compiler.nqp:364  (/Users/liz/Github/rakudo/install/share/nqp/lib/NQPHLL.moarvm:command_eval)
 from src/Perl6/Compiler.nqp:233  (/Users/liz/Github/rakudo/install/share/perl6/lib/Perl6/Compiler.moarvm:command_eval)
 from NQP::src/HLL/Compiler.nqp:289  (/Users/liz/Github/rakudo/install/share/nqp/lib/NQPHLL.moarvm:command_line)
 from src/main.nqp:81  (/Users/liz/Github/rakudo/install/share/perl6/runtime/perl6.moarvm:MAIN)
 from src/main.nqp:63  (/Users/liz/Github/rakudo/install/share/perl6/runtime/perl6.moarvm:<mainline>)
 from <unknown>:1  (/Users/liz/Github/rakudo/install/share/perl6/runtime/perl6.moarvm:<main>)
 from <unknown>:1  (/Users/liz/Github/rakudo/install/share/perl6/runtime/perl6.moarvm:<entry>)