如何判断某个节点是否存在？

string DestinationMapFile = @"D:\ATS\Application\C#\Respos\GitHubFirstTest\HelloWorld\ConsoleApp\bin\Debug\31005023347801060010318094853001.xml";
XmlDocument xmlFile = new XmlDocument();
xmlFile.Load(DestinationMapFile);
if (xmlFile.SelectSingleNode("//layerInfo") != null)
{
    xmlFile.SelectSingleNode("//layerInfo").RemoveAll();
}
if (xmlFile.SelectSingleNode("//CardID") != null)
{
    xmlFile.SelectSingleNode("//CardID").RemoveAll();
}