String encoding not working

I am trying to encode a utf16 string in protodef but when I do

"string": [
  "pstring", {
    "countType": "u16"
  }
]

it will encode a utf8 string and when I add

"string": [
  "pstring", {
    "countType": "u16",
    "encoding": "utf16"
  }
]

it will just give a validation error

Here is the validation error in case you need it:

{
  "keyword": "enum",
  "dataPath": "",
  "schemaPath": "#/oneOf/0/enum",
  "params": {
    "allowedValues": [
      "native"
    ]
  },
  "message": "should be equal to one of the allowed values",
  "schema": [
    "native"
  ],
  "parentSchema": {
    "enum": [
      "native"
    ]
  },
  "data": [
    "pstring",
    {
      "countType": "u16",
      "encoding": "utf16"
    }
  ]
}

Start by locating the pstring type's validation and encoding handling, using the reported countType and encoding options as search terms. Reproduce the utf16 configuration and validation error, then confirm that the accepted configuration encodes utf16 data as requested.