https://github.com/opscode/chef/blob/master/lib/chef/encrypted_data_bag_item.rb#L85

gistfile1.rb

  def self.load(data_bag, name, secret = nil) #secret can be nil
    raw_hash = Chef::DataBagItem.load(data_bag, name) #load the raw (encrypted) hash into a databag object
    secret = secret || self.load_secret #if secret is specified, this or operator short circuits and returns the first value. if secret is nil, calls self.load secret (L7)
    self.new(raw_hash, secret) #return a new object
  end

  def self.load_secret(path=nil) #again, path can be nil
    path ||= Chef::Config[:encrypted_data_bag_secret] # a shortcut to saying path = path || Chef::Config... as L3
    if !path #nothing in path, means the default secret location wasn't set either. are you seeing this error?
      raise ArgumentError, "No secret specified to load_secret and no secret found at #{Chef::Config.platform_specific_path('/etc/chef/encrypted_data_bag_secret')}"
    end