.isEmpty
,
.nonEmpty
or .isDefined.
!seq.isEmpty -> seq.nonEmpty
seq.size == 0 -> seq.isEmpty
seq.size != 0 -> seq.nonEmpty
!(seq.length > 1) -> seq.isEmpty
seq.exists(_ => true) -> seq.nonEmpty
seq.exists(const(true)) -> seq.nonEmpty
!option.isEmpty -> option.isDefined
option == None -> option.isEmpty
option != None -> option.isDefined