[perl #123969] NullPointerException on jvm for same CStruct in CStruct

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# New Ticket Created by  Tobias Leich 
# Please include the string:  [perl #123969]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=123969 >


$ perl6-m -e 'class Foo is repr<CStruct> { has int32 $.idontcare; has
Foo $.bar }'

$ perl6-j --ll-exception -e 'class Foo is repr<CStruct> { has int32
$.idontcare; has Foo $.bar }'
java.lang.NullPointerException
  in compose_repr (gen/jvm/Metamodel.nqp:1440)
  in compose (gen/jvm/Metamodel.nqp:2770)
  in pkg_compose (src/Perl6/World.nqp:1938)
  in package_def (gen/jvm/Perl6-Actions.nqp:1956)
  in !reduce (gen/jvm/stage2/QRegex.nqp:1241)
  in !cursor_pass (gen/jvm/stage2/QRegex.nqp:1202)
  in package_def (src/Perl6/Grammar.nqp:2445)
  in package_declarator:sym<class> (src/Perl6/Grammar.nqp)
  in !protoregex (gen/jvm/stage2/QRegex.nqp:1278)
  in package_declarator (src/Perl6/Grammar.nqp)
  in term:sym<package_declarator> (src/Perl6/Grammar.nqp)
  in !protoregex (gen/jvm/stage2/QRegex.nqp:1278)
  in term (src/Perl6/Grammar.nqp)
  in termish (src/Perl6/Grammar.nqp:3724)
  in EXPR (gen/jvm/stage2/NQPHLL.nqp:558)
  in EXPR (src/Perl6/Grammar.nqp:3755)
  in statement (src/Perl6/Grammar.nqp:1338)
  in statementlist (src/Perl6/Grammar.nqp:1270)
  in LANG (gen/jvm/stage2/NQPHLL.nqp:771)
  in FOREIGN_LANG (src/Perl6/Grammar.nqp:1681)
  in comp_unit (src/Perl6/Grammar.nqp:1128)
  in TOP (src/Perl6/Grammar.nqp:368)
  in parse (gen/jvm/stage2/QRegex.nqp:1872)
  in parse (gen/jvm/stage2/NQPHLL.nqp:1440)
  in compile (gen/jvm/stage2/NQPHLL.nqp:1396)
  in eval (gen/jvm/stage2/NQPHLL.nqp:1138)
  in  (gen/jvm/stage2/NQPHLL.nqp:1244)
  in command_eval (gen/jvm/stage2/NQPHLL.nqp:1241)
  in command_eval (src/Perl6/Compiler.nqp:17)
  in command_line (gen/jvm/stage2/NQPHLL.nqp:1226)
  in MAIN (gen/jvm/main.nqp:39)
  in <mainline> (gen/jvm/main.nqp:35)
  in  (gen/jvm/main.nqp)