mechanize：Mechanize::FileResponse#read_body

everyday Ruby 
>> require 'mechanize/file_response'
=> true
>> open("foo").read
=> "abc"
>> x = Mechanize::FileResponse.new("foo")
=> #<Mechanize::FileResponse:0xb7bc78a4 @file_path="foo">
>> x.read_body
>> x.read_body
LocalJumpError: no block given
	from /usr/local/ruby-1.8.7/lib/ruby/gems/1.8/gems/mechanize-1.0.0/lib/mechanize/file_response.rb:14:in `read_body'
	from (irb):4
>> x.read_body {|xx| puts xx}
abc
=> nil
>> x = Mechanize::FileResponse.new("foo_dir")
=> #<Mechanize::FileResponse:0xb7bb8700 @file_path="foo_dir">
>> x.read_body {|xx| puts xx}
<html><body></body></html>
=> nil