Safely access an element in a nested hash by its path.

hash_at.rb

class Hash
  # Safely access an element in a nested hash by its path.
  # If any of the intervening hashes is not present, nil is returned.
  def at(*path)
    val = self
    path.each do |k|
      val = val[k]
      return nil unless val
    end
    val
  end
end