Optional
Optimistic-concurrency precondition: if set to a non-empty value that does not match the resource's current etag, the update is rejected as a conflict (HTTP 409). Omit this field or send an empty string to update unconditionally.
etag
Optimistic-concurrency precondition: if set to a non-empty value that does not match the resource's current
etag, the update is rejected as a conflict (HTTP 409). Omit this field or send an empty string to update unconditionally.