How to check cursor null or not in android?

I'm trying to check values of field ID in BangCauHoi table. This is my function:

public boolean checkID(String ndCauHoi){
        boolean check = true;
        String query = "select ID from BangCauHoi where CauHoi=?";
        Cursor c = database.rawQuery(query, new String[] { ndCauHoi });
        if (c != null)
        {
             c.moveToFirst();
                 if (c.isNull(c.getColumnIndex("ID")))
                 {
                     check = false;
                 }
        }
         c.close();
    return check;
}

And result:

java.lang.RuntimeException: Unable to start activity ComponentInfo{us.datn_02/us.datn_02.ShowQuestion}: android.database.CursorIndexOutOfBoundsException: Index 0 requested, with a size of 0

Somebody can help me please?

if I change my code to:

public boolean checkID(String ndCauHoi){
        boolean check = true;
        String query = "select ID from BangCauHoi where CauHoi=?";
        Cursor c = database.rawQuery(query, new String[] { ndCauHoi });
        if (c.moveToFirst())
        {
                 if (c.isNull(c.getColumnIndex("ID")))
                 {
                     check = false;
                 }
        }
         c.close();
    return check;
}

then it always return true even field ID have no value with this where clause.

Help me please!... Sorry because my english.