AutocompletetextView crash passing string not from ItemSelection

I have an adapter in which there are some values. I can choose one of this value from a AutoCompleteTextView and then i can pass the value in a next activity when i click on a button. Typing something it shows the possible result. Of course, if i click on one of them it adds the value in the AutoCompletetextView and this is the code so far:

firstAutocomplete.setAdapter(adapter);
        firstAutocomplete.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                firstAutocomplete.showDropDown();
            }
        });

firstAutocomplete.setOnItemClickListener(new OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
                itemFirst = adapter.getItem(arg2);
            }
        });

The adapter of course contains the values. It works normally in this way. My problem now is that i can save the value i choose in a sqLite db and i shows this value in a dynamic listview. What i want is that if i click a listview item it add that value on the AutoCompleteTextView so i can easily go to next activity without typing each time.

Problem: If i do in this way:

lv.setOnItemClickListener(new OnItemClickListener() {
             public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

                   Cursor cursor = (Cursor) parent.getItemAtPosition(position);
                   String item_first = cursor.getString(cursor.getColumnIndex(mdb.KEY_FIRST));
                   firstAutocomplete.setText(item_first);

             }
         });

and the i click the button tha app crashes because seems that the value firstAutocomplete.setText(item_first); is null.

My question is: Is the problem due to the fact that the setText not is "forced" and not a value directly choose from the adapter and so it found a null string? How can i solve?