How to check the NULL value in NSString in iOS?

Question

I have an NSString and I want to check if it has a NULL value. If it does, then the if condition should execute. Else it should execut

Answer 1

  NSString *str;

  if ([[str stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]]          isEqualToString:@""] || str==nil) 
  {

  }