空字符串的统一处理

• (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:@""]) {
newStr = @"";
}
return newStr;
}