判断字符串为空 ""

背后台坑过
后台给的同一个数据 有 ""

• (BOOL) isBlankString:(NSString *)string {
  if (string == nil || string == NULL) {
  return YES;
  }
  if ([string isKindOfClass:[NSNull class]]) {
  return YES;
  }
  if ([[string stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]] length]==0) {
  return YES;
  }
  return NO;
  }