meck 使ってるとこの部分のエラーが出てしまう

cover.erl

%% Removes a module from the list of imported modules and writes a warning      
%% This is done when a module is compiled.
remove_imported(Module,Imported) ->
    case lists:keysearch(Module,1,Imported) of
        {value,{Module,_,ImportFiles}} ->
            io:fwrite("WARNING: Deleting data for module ~w imported from~n"
                      "~p~n",[Module,ImportFiles]),
            lists:keydelete(Module,1,Imported);
        false ->
            Imported
    end.