Hash extension for safe access to possibly undefined elements

hash_extension.rb

class Hash
  def value_at(*keys)
    begin
      memo = self.dup
      keys.each { |key| memo = memo[key] }
      memo
    rescue
      nil
    end
  end
end

hsh = { :parent => { :child => 'sally' }}

puts hsh.value_at :parent, :child   # => 'sally'
puts hsh.value_at :foo, :bar        # => nil