class Roda::RodaPlugins::TypecastParams::Params

def array!(type, key, default=nil)

the returned array is +nil+, raise an Error.
Call +array+ with the +type+, +key+, and +default+, but if the return value is nil or any value in 
def array!(type, key, default=nil)
  v = array(type, key, default)
  if key.is_a?(Array)
    key.zip(v).each do |k, arr|
      check_array!(k, arr)
    end
  else
    check_array!(key, v)
  end
  v
end