Before check formatting style, make sure was declared in configuration

lib/click_to_globalize.rb

@@ -90,6 +90,7 @@ def observers # :nodoc:
       #   * textile (RedCloth gem)
       #   * markdown (BlueCloth gem)
       def formatting
+        return unless configuration['formatting']
         @@formatting ||= case configuration['formatting'].to_sym
           when :textile  then textile?  ? :textile  : nil
           when :markdown then markdown? ? :markdown : nil