iphone - Rate the app functionality in ios not working well -

i having app in have button "rate" app.

on click of button, using following code.

- (ibaction)ratepressed:(id)sender {       nsstring *str = @"itms-apps://ax.itunes.apple.com/webobjects/mzstore.woa";     str = [nsstring stringwithformat:@"%@/wa/viewcontentsuserreviews?", str];     str = [nsstring stringwithformat:@"%@type=purple+software&id=", str];      // here app id itunesconnect      str = [nsstring stringwithformat:@"%@appid", str];     nslog(@"str %@",str);      [[uiapplication sharedapplication] openurl:[nsurl urlwithstring:str]];  } 

my app not on app store when pressed rate button gives me error saying

your request produced error. [new nullresponse]

when put appid of of app on appstore. works fine.

so can put custom message saying "app not available"? when app not on appstore. or default message apple?

please me.