Set default ring tone to contact

Question

we need to set custom ringtone to a specific contact and set it back to the default ring tone after some time . Problem is, that on some devices when we put null into database, this devices set ringtone to "unknown". (Device example: Nexus 4)

ContentValues values = new ContentValues();
values.putNull(ContactsContract.Contacts.CUSTOM_RINGTONE);
                    context.getContentResolver().update(Contacts.CONTENT_URI,
                            values, "_ID=?",
                            new String[] { String.valueOf(c.id) });

Is there any other way how to set default ringtone to contact?

Answer 1

Ok, problem was elsewhere. It was used ringtone from assets and this cause "unknown ringtone" problem. Solved by copy ringtone in to device.