Fix a nil input bug in the wiki helper

helpers.rb

@@ -21,7 +21,7 @@ def recipe_category_link(recipe, category)
     end
 
     def wiki(original)
-      text = original.dup
+      text = (original || '').dup
       text.gsub!(/\b(\d+)F/, "\\1° F")
       text.gsub!(/\[kid:(\w+)\]/m) { |kid| kid_nicknames[$1] }
       text.gsub!(/\[recipe:(\S+)\]/m) { |r| recipe_link($1) }

spec/eee_helpers_spec.rb

@@ -5,6 +5,10 @@
     wiki("bob").should contain("bob")
   end
 
+  it "should return an empty string if called with nil" do
+    wiki(nil).should == ""
+  end
+
   it "should convert textile to HTML" do
     textile = <<_TEXTILE
 paragraph 1 *bold text*