if (![mutableRequest valueForHTTPHeaderField:@"Content-Type"]) {
        [mutableRequest setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
    }

warning 這裡修改了源碼

    if ([parameters isKindOfClass:[NSString class]]) {
        [mutableRequest setHTTPBody:[parameters dataUsingEncoding:self.stringEncoding]];
    } else {
        [mutableRequest setHTTPBody:[query dataUsingEncoding:self.stringEncoding]];
    }