Allow for case where no readers are found.

Author: gkellogg

lib/rdf/cli.rb

@@ -506,7 +506,7 @@ def self.exec(args, output: $stdout, option_parser: nil, messages: {}, **options
       end
 
       if options[:statistics]
-        options[:statistics][:reader] = @readers.first unless @readers.empty?
+        options[:statistics][:reader] = @readers.first unless (@readers || []).empty?
         options[:statistics][:count] = @repository.count
       end
     end