Playground doesn't appear to support the ? and ??, chaining and coalescing operators

Trying out the https://expr-lang.org/playground to test out chaining and the playground doesn't appear to support these options. The output window shows errors rather than returning nil when trying out nil coallecsing and chaining. Even the example built in to the playground doesn't appear to work.

Trying out input:

   {"status": "4","thing":{}}

Test expr code

   thing?.name

Returns

  unknown field name (1:8)
  | thing?.name

Shouldn't the response be nil?