Deleting keys in Thread metadata

Is it possible to delete keys in the metadata for a thread? It seems you can only update the value of a key for the metadata via the update endpoint POST https://api.openai.com/v1/threads/{thread_id}.

It appears not. Going beyond an empty string where it remains, sending JSON null fails as one guess of how you might do it:

{
ā€œerrorā€: {
ā€œmessageā€: ā€œInvalid type for ā€˜metadata.mykey’: expected a string, but got null instead.ā€,
ā€œtypeā€: ā€œinvalid_request_errorā€,
ā€œparamā€: ā€œmetadata.modifiedā€,
ā€œcodeā€: ā€œinvalid_typeā€
}
}

yeah I’ve tried everything. Seems odd considering the threads can persist indefinitely.