Replaces code, which emulates .flatten method on collections of collections.

Before:

Seq(Seq(1), Seq(2), Seq(2)).flatMap(identity)
Seq(Seq(1, 2, 3), Seq(4, 5), Seq(6, 7)).flatMap(x => identity(x))
Seq(Seq(2, 7, 1), Seq(8, 2), Seq(8, 1)).flatMap(x => x)
Set(Set(1), Set(2), Set(3)).flatMap(x => x)

nestedOption.getOrElse(None)
nestedOption.map(_.get)

After:
Seq(Seq(1), Seq(2), Seq(2)).flatten
Seq(Seq(1, 2, 3), Seq(4, 5), Seq(6, 7)).flatten
Seq(Seq(2, 7, 1), Seq(8, 2), Seq(8, 1)).flatten
Set(Set(1), Set(2), Set(3)).flatten

nestedOption.flatten
nestedOption.flatten