create document only if it doesn't already exists

[rahulserver]

Based on the comment that closed the issue #1203
"(you can now use SetOptions to achieve the desired behaviour above)"

I don't understand how can we use "SetOptions" https://pub.dev/documentation/cloud_firestore_platform_interface/latest/cloud_firestore_platform_interface/SetOptions-class.html
as a replacement to the .create in the nodejs sdk. ( https://googleapis.dev/nodejs/firestore/latest/DocumentReference.html#create )

The setoptions can only allow us to turn merge:true which will cause the .set to "only replace the values specified in its data argument". This will not fail and throw error like the .create in nodejs. (Hence does not answer the original question which wants to ensure that the document is never overwritten)

Consequently .set with SetOptionswill be less efficient as for ensuring that a doc does not exist, i will have to put a separate query before trying to create a new document.