i Hav also modified the definition in my controllers as follows:
@categories = category.find(:all)
That should be Category.find(:all)
You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.map
seems there something i dont get
You have not said where that error occurs, but wherever it is
something is nil. Have a look at the Rails Guide on Debugging, that
will show you how to use ruby-debug to break into code, inspect data
and follow the flow. Then when you get this sort of error you can put
in breakpoints and check each of the variables to find which one is
nil.