reactivemongo.api.commands.IsMasterCommand
(Since version 0.19.1) No longer a case class
(Since version 0.18.5) Use the constructor with lastWrite
(Since version 0.19.1) Use the constructor with tag map
the unique identifier for each election, or -1
the set version, or -1 if unknown
(Since version 0.19.1) No longer a case class