Using Checkbox and Filterable in RecycleView Android

I'm creating a project, that uses a webservice to fetch the number of departments and there names and creates dynamic checkboxs. Then I'm using filterable to filter the adapter , by checking from sharedpreferences if the checkbox is checked if not checked I try to hide it from the adapter (TicketsActivity):

for (int i=0;i<filterList.size();i++) {
    if (!getFromSP(filterList.get(i) + i)) {
       mAdapter.getFilter("Department").filter(filterList.get(i).toLowerCase());
    }
}

and afther that

if (recyclerView.getAdapter() == null) {
    mAdapter.notifyItemRangeInserted(0,ticketList.size()-1);
    recyclerView.setAdapter(mAdapter);
} else {
   recyclerView.getAdapter().notifyItemRangeInserted(0,ticketList.size()-1);
}

And in my custom Adapter (TicketsAdapter):

public Filter getFilter(final String type) {
    return new Filter() {
        @Override
        protected FilterResults performFiltering(CharSequence charSequence) {
            String charString = charSequence.toString();
            if (charString.isEmpty()) {
                ticketListFiltered = ticketList;
            } else if (type.equals("Search")) {
                List<Ticket> filteredList = new ArrayList<>();
                for (Ticket row : ticketList) {
                    if (row.getTitle().toLowerCase().contains(charSequence) || row.getDate().toLowerCase().contains(charSequence) || row.getPriority().toLowerCase().contains(charSequence)) {
                        filteredList.add(row);
                    }
                }
                ticketListFiltered = filteredList;
            } else {
                List<Ticket> filteredList;
                filteredList = ticketList;
                for (Ticket row : ticketList) {
                    if (row.getDepartment().toLowerCase().contains(charSequence)) {
                        filteredList.remove(row);
                    }
                }
                ticketListFiltered = filteredList;
            }
            FilterResults filterResults = new FilterResults();
            filterResults.values =ticketListFiltered;
            return filterResults;
        }
@Override
public int getItemCount() {
    return ticketListFiltered.size();
}

However this throws an Exception on 'int java.util.List.size()' getItemCount, if i change the filteredList.remove(row) to filteredList.add(row) it will work find,but i need to remove from the adapter rows with "unchecked" department. I can't find what i'm doing wrong. Btw this works fine with SearchView