why indicator line empty value ?

Hi,

I'm trying to write this indicator with 2 colors: up red, down white. But why the result is total empty?

//+------------------------------------------------------------------+
//|                                                       macdup.mq4 |
//|                        Copyright 2013, MetaQuotes Software Corp. |
//|                                        http://www.metaquotes.net |
//+------------------------------------------------------------------+
#property copyright "Copyright 2013, MetaQuotes Software Corp."
#property link      "http://www.metaquotes.net"
#property indicator_color1 White
#property indicator_color2 Red

//---- input parameters
extern int fast_ema_period=12;
extern int slow_ema_period=26;
extern int signal_period=9;

double Ext1Buffer[];
double Ext2Buffer[];
double Ext3Buffer[];

#property indicator_separate_window
//+------------------------------------------------------------------+
//| Custom indicator initialization function                         |
//+------------------------------------------------------------------+
int init()
  {
//---- indicators
   SetIndexDrawBegin(0,slow_ema_period);
SetIndexDrawBegin(1,slow_ema_period);

//---- 4 indicator buffers mapping
   SetIndexBuffer(0,Ext1Buffer);
SetIndexBuffer(1,Ext2Buffer);


//---- drawing settings
   SetIndexStyle(0,DRAW_HISTOGRAM);
   SetIndexStyle(1,DRAW_HISTOGRAM);
//----
   return(0);
  }
//+------------------------------------------------------------------+
//| Custom indicator deinitialization function                       |
//+------------------------------------------------------------------+
int deinit()
  {
//----
   
//----
   return(0);
  }
//+------------------------------------------------------------------+
//| Custom indicator iteration function                              |
//+------------------------------------------------------------------+
int start()
  {
  int tfup;
  switch(Period())
  {
  case 5:
    tfup = 30;
    break;
  case 15:
    tfup = 60;
    break;
  case 30:
    tfup = 240;
    break;
  case 60:
    tfup = 240;
    break;
  case 240:
    tfup = 1440;
    break; 
  default:
    tfup = 240;
    break;                 
  }
  
   int limit;
   int counted_bars=IndicatorCounted();
//---- check for possible errors
   if(counted_bars<0) return(-1);
//---- last counted bar will be recounted
   if(counted_bars>0) counted_bars--;
   limit=Bars-counted_bars;
//---- main loop

   for(int i=0; i<limit; i++)
     {

     Ext3Buffer[i]=iMACD(NULL, tfup, fast_ema_period, slow_ema_period, signal_period, PRICE_CLOSE,MODE_MAIN,i);
     }
     
      for( i=0; i<limit-1; i++)
     {
     if(Ext3Buffer[i]>Ext3Buffer[i+1])   
       {     Ext2Buffer[i]=Ext3Buffer[i];
             Ext1Buffer[i]=EMPTY_VALUE;
        }
     if(Ext3Buffer[i]<Ext3Buffer[i+1])   
       {     Ext1Buffer[i]=Ext3Buffer[i];
             Ext2Buffer[i]=EMPTY_VALUE;
        }       
     if(Ext3Buffer[i]==Ext3Buffer[i+1])   
       {     Ext2Buffer[i]=EMPTY_VALUE;
             Ext1Buffer[i]=EMPTY_VALUE;
        }       
       

     }  
//----
   return(0);
  }
//+------------------------------------------------------------------+