Ruby’s Array#first will have very different return types based on what arguments you provide. Without an argument, it will return nil or object. With an argument, it will always return a new array; even if your argument is 1 or 0.
a = [:foo, 'bar', 2]
a.first
# => :foo
a.first(1)
# => [:foo]
a.first(0)
# => []
With an empty array:
[].first
# => nil
[].first(1)
# => []
[].first(0)
# => []