XML-Simple ArgumentError / README example broken

[jm3]

The README example fails after the third line (user = flickr.users(...) with
an XML-Simple ArgumentError:

ruby-2.4.2/gems/xml-simple-1.1.5/lib/xmlsimple.rb:996:in `find_xml_file': File does not exist: . (ArgumentError)
from ~/.rvm/gems/ruby-2.4.2/gems/xml-simple-1.1.5/lib/xmlsimple.rb:168:in `xml_in'
from ~/.rvm/gems/ruby-2.4.2/gems/xml-simple-1.1.5/lib/xmlsimple.rb:203:in `xml_in'
from ~/.rvm/gems/ruby-2.4.2/gems/flickr-1.0.2/flickr.rb:66:in `request'
from ~/.rvm/gems/ruby-2.4.2/gems/flickr-1.0.2/flickr.rb:148:in `method_missing'
from ~/.rvm/gems/ruby-2.4.2/gems/flickr-1.0.2/flickr.rb:120:in `rescue in users'
from ~/.rvm/gems/ruby-2.4.2/gems/flickr-1.0.2/flickr.rb:120:in `users'
from comments.rb:8:in `<main>'

Gemfile.lock:

GEM
  remote: https://rubygems.org/
  specs:
    coderay (1.1.2)
    dotenv (2.6.0)
    flickr (1.0.2)
      xml-simple (>= 1.0.7)
    method_source (0.9.2)
    pry (0.12.2)
      coderay (~> 1.1.0)
      method_source (~> 0.9.0)
    xml-simple (1.1.5)