function - Filter out null string in a list of lists -

currently have function:

removenull strlist = filter (not . null) strlist 

but need use map (i assume) apply list of lists, i'm getting type errors.

in ghci, functions filters correctly:

removenull ["i", "", "b"] ["i","b"] 

but doesn't filter:

removenull [["i", "", "b"], ["i", "", "b"]] [["i","","b"],["i","","b"]] 

simply use map apply filter each sublist, e.g.

removenull strlist = map (filter (not . null))  strlist                    //^^^ see here