BUG: parser returned null output even though parsing did not fail

[MeAmAnUsername]

Summary

List elements with indent and offside constraint result in error in the title

What you did

Grammar:

context-free start-symbols
  Exp
context-free sorts
  Exp
context-free syntax
  Exp.Num = NAT
  Exp.List = <[<elems:{Exp ", "}*>]>
    {layout(indent "[" elems && offside "[" elems)}

lexical sorts NAT
lexical syntax
  NAT = [0-9]+
lexical restrictions
  NAT -/- [0-9]
lexical syntax
  LAYOUT = [\ \n\t\v\f\r]
context-free restrictions
  LAYOUT? -/- [\ \n\t\v\f\r]

File:

[
 1,
2,
3
]

What you expected to happen

Parses successfully

What actually happened

Parsing fails with error: java.lang.RuntimeException: BUG: parser returned null output even though parsing did not fail

Context

• Spoofax version: Spoofax-pie 0.19.2
• Operating system & version: MacOS Mojave, 10.14.6 (18G9323)
• Java version (if applicable): 11 (bundled with Spoofax)
• Eclipse version (if applicable): 4.23.0.20220310-1200
• Gradle version (if applicable): N.A.

Additional information

Error log:

java.lang.RuntimeException: BUG: parser returned null output even though parsing did not fail
	at mb.jsglr1.common.JSGLR1Parser.parse(JSGLR1Parser.java:52)
	at mb.rpgdsl.RpgdslParser.parse(%2Frpgdsl%2Fbuild%2Fgenerated%2Fsources%2Flanguage%2Fmb%2Frpgdsl%2FRpgdslParser.java:19)
	at mb.rpgdsl.task.RpgdslParse.parse(%2Frpgdsl%2Fbuild%2Fgenerated%2Fsources%2Fadapter%2Fmb%2Frpgdsl%2Ftask%2FRpgdslParse.java:50)
	at mb.jsglr.pie.JsglrParseTaskDef.exec(JsglrParseTaskDef.java:102)
	at mb.jsglr.pie.JsglrParseTaskDef.exec(JsglrParseTaskDef.java:22)
	at mb.pie.api.Task.exec(Task.java:56)
	at mb.pie.runtime.exec.TaskExecutor.execInternal(TaskExecutor.java:130)
	at mb.pie.runtime.exec.TaskExecutor.exec(TaskExecutor.java:87)
	at mb.pie.runtime.exec.BottomUpRunner.exec(BottomUpRunner.java:419)
	at mb.pie.runtime.exec.BottomUpRunner.execAndSchedule(BottomUpRunner.java:132)
	at mb.pie.runtime.exec.BottomUpRunner.execScheduled(BottomUpRunner.java:119)
	at mb.pie.runtime.exec.BottomUpRunner.requireInitial(BottomUpRunner.java:82)
	at mb.pie.runtime.MixedSessionImpl.lambda$updateAffectedBy$0(MixedSessionImpl.java:72)
	at mb.pie.runtime.SessionImpl.handleException(SessionImpl.java:233)
	at mb.pie.runtime.MixedSessionImpl.updateAffectedBy(MixedSessionImpl.java:72)
	at mb.spoofax.eclipse.pie.PieRunner.updateAffectedBy(PieRunner.java:509)
	at mb.spoofax.eclipse.pie.PieRunner.addOrUpdateEditor(PieRunner.java:144)
	at mb.spoofax.eclipse.editor.EditorUpdateJob.update(EditorUpdateJob.java:112)
	at mb.spoofax.eclipse.editor.EditorUpdateJob.run(EditorUpdateJob.java:79)
	at org.eclipse.core.internal.jobs.Worker.run(Worker.java:63)