AppSync Emulator - emulator does not enforce strict JSON in VTL templates

[cbaron]

{
  "version" : "2017-02-28",
  "operation" : "PutItem",
  "key": {
      "type" : { "S": "Ingredient" },
      "position" : { "N": "$ctx.args.input.position" },
  },
  "attributeValues": {
    "name" : { "S": "$ctx.args.input.name" },
    composition: $util.dynamodb.toMapJson($ctx.args.input.composition),
  }
}

Works in the emulator, but not when deployed to AWS -- composition must be wrapped in double quotes:

{
  "version" : "2017-02-28",
  "operation" : "PutItem",
  "key": {
      "type" : { "S": "Ingredient" },
      "position" : { "N": "$ctx.args.input.position" },
  },
  "attributeValues": {
    "name" : { "S": "$ctx.args.input.name" },
    "composition": $util.dynamodb.toMapJson($ctx.args.input.composition),
  }
}

[lightsofapollo]

HRRRM Okay... So the they are not using json 5 but are not using strict json either (trailing commas are fine). Not quite sure right path is here. more investigation needed!