the fetch method is aliased to the  method which in turn isn't compatible with the ruby Hash API. We've used specifically the second parameter to fetch to provide a sensible default if the key is not set, aliasing fetch to  means it no longer takes this second parameter.
The method signature for fetch looks like this:
fetch(key [, default] )
You can either supply just the key to fetch or the key and a default if no key or a block which would be called if no key present.