    # File lib/rbot/maskdb.rb, line 149
        def find(iu)
          debug "find(#{iu.fullform})"
          iud = iu.downcased
          matches = @tree.find(iud.host, iud.user, iud.nick).uniq.map do |val|
            m = metric(iu, *val)
            m ? [val[0], m] : nil
          end.compact.sort { |a, b| a[1] <=> a[1] }
          debug "matches: " + (matches.map do |m|
            "#{m[0].username}: [#{m[1]}]"
          end.join(', '))
          return matches.empty? ? nil : matches[0][0]
        end