空字符串的统一处理

<code>

• (NSString *)replaceNullValue:(NSString *)string
  {
  NSString *newStr = [NSString stringWithFormat:@"%@", string];
  if ([newStr isKindOfClass:[NSNull class]] ||
  newStr == nil ||
  [newStr isEqualToString:@"(null)"] ||
  [newStr isEqualToString:@""] ||
  [newStr isEqualToString:@"null"] ||
  [newStr isEqualToString:@"<null>"]) {
  newStr = @"";
  }
  return newStr;
  }
  </code>