how to use where clause in cursor query in sqlite

I want only particular rows that has "E" inside the column "TX_IDT". I used the following code but apps stops. In logcat the error says it is at db.query line.

public Cursor getAllRows( ) {        
String where = null;    
SQLiteDatabase db =    helper.getReadableDatabase();    
String[] columns = { VivzHelper.UID, helper.UID,helper.NAME,helper.TX_IDT};     
String whereClause = "TX_IDT = ? ";    
String[] whereArgs = new String[] {  "E"  };    
Cursor c = db.query( VivzHelper.TABLE_NAME,   columns,whereClause,whereArgs,           null, null, NAME + " ASC"); // for out btn    
    if (c != null) {    
        c.moveToFirst();    
    }    
    return c;    
}    

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