Suggestion for `orNull`: ```fun <A> Arb<...

# kotest-contributors

[LeoColman]

Suggestion for `orNull`:

fun <A> Arb<A>.orNull(nullChance: Double = 0.25): Arb<A?> = arb(this.edgecases().plus(null as A?)) { rs ->
   sequence {
      while (true)
         yield(if (rs.random.nextDouble() <= nullChance) null else <mailto:[e-mail]|[e-mail]>(rs))
    }
}