我想解析示例中結構化的XML片段。我一直遇到值是空的。這是我正在使用的簡化版本，僅用于顯示問題。package mainimport (        "encoding/xml"        "fmt")type Entry struct {        VulnCveId   string  `xml:"entry>vuln:cve-id"`}func main() {        v := Entry{}        err := xml.Unmarshal([]byte(data), &v)        if err != nil {                fmt.Printf("error: %v", err)                return        }        fmt.Println(v.VulnCveId)}const data = `  <entry id="CVE-2005-4895">    <vuln:vulnerable-configuration id="http://nvd.nist.gov/">      <cpe-lang:logical-test negate="false" operator="OR">        <cpe-lang:fact-ref name="cpe:/a:csilvers:gperftools:0.3" />        <cpe-lang:fact-ref name="cpe:/a:csilvers:gperftools:0.2" />        <cpe-lang:fact-ref name="cpe:/a:csilvers:gperftools:0.1" />      </cpe-lang:logical-test>    </vuln:vulnerable-configuration>    <vuln:vulnerable-software-list>      <vuln:product>cpe:/a:csilvers:gperftools:0.3</vuln:product>      <vuln:product>cpe:/a:csilvers:gperftools:0.1</vuln:product>      <vuln:product>cpe:/a:csilvers:gperftools:0.2</vuln:product>    </vuln:vulnerable-software-list>    <vuln:cve-id>CVE-2005-4895</vuln:cve-id>    <vuln:published-datetime>2012-07-25T15:55:01.273-04:00</vuln:published-datetime>    <vuln:last-modified-datetime>2012-08-09T00:00:00.000-04:00</vuln:last-modified-datetime>    <vuln:cvss>      <cvss:base_metrics>        <cvss:score>5.0</cvss:score>        <cvss:access-vector>NETWORK</cvss:access-vector>        <cvss:access-complexity>LOW</cvss:access-complexity>        <cvss:authentication>NONE</cvss:authentication>        <cvss:confidentiality-impact>NONE</cvss:confidentiality-impact>        <cvss:integrity-impact>NONE</cvss:integrity-impact>        <cvss:availability-impact>PARTIAL</cvss:availability-impact>        <cvss:source>http://nvd.nist.gov</cvss:source>v.VulnCveId在此實例中為空。我究竟做錯了什么？