showMissing property
If the list should show missing documents.
A document is missing if it does not exist, but there are sub-documents
nested underneath it. When true, such missing documents will be returned
with a key but will not have fields,
google.firestore.v1.Document.create_time, or
google.firestore.v1.Document.update_time set.
Requests with show_missing may not specify where or order_by.
Implementation
final bool showMissing;