first_token_time is when the first output token was produced (RFC3339 date-time), when
recorded for streamed runs.
public Optional<OffsetDateTime> firstTokenTime()first_token_time is when the first output token was produced (RFC3339 date-time), when
recorded for streamed runs.
LangChainInvalidDataException: if the JSON field has an unexpected type (e.g. if the
server responded with an unexpected value).