It looks like if you have more than one parameter with the designation "isnamevar" then the type is expecting that you provide a title_pattern method that allows puppet to uniquely identify the resource. I'm mostly guessing at this based on a little web searching and grepping in /opt/puppetlabs/puppet/lib/ruby/vendor_ruby/puppet/type

and this explanation may help: https://www.mail-archive.com/puppet-users@googlegroups.com/msg24766.html