Earlier quoted context omitted.
I've seen this in Ruby and Elixir that drives me a little nuts: if !is_nil(foo)
While it may not matter in many circumstances, this is not the same as "if foo", because false is not nil.
It's true but in 10+ years of writing Ruby it hasn't mattered in _any_ circumstances I've come across. I also assert that having a boolean where `nil` is meaningfully different than `false` is a smell and should be avoided.