尝试返回文档时出现对象错误（Umbraco Document API）

Question

我正在处理递归方法，该方法显示我有权查看的所有文档。第一遍的伟大工程，但是当它递归调用自己通过当前文档的儿童的文件阵列，它抛出一个错误：

Object reference not set to an instance of an object. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

下面的代码：

protected void Page_Load(object sender, EventArgs e) 
{ 
    lblTest.Text = "Data<br /><br />"; 
    Document[] releaseDocs = Document.GetRootDocuments(); 
    displayDocs(releaseDocs); 
} 
public void displayDocs(Document[] releaseDocs) 
{ 
    string docPermissions = null; 
    User currentUser = User.GetCurrent(); 
    foreach (var doc in releaseDocs) 
    { 
     docPermissions = currentUser.GetPermissions(doc.Path); 
     if ((docPermissions.Contains("F")) && (docPermissions.Contains("U"))) 
     { 
      lblTest.Text += "D/T: " + doc.CreateDateTime + "<br />\r\n"; 
      lblTest.Text += "Level: " + doc.Level + "<br />\r\n"; 
      lblTest.Text += "Text: " + doc.Text + "<br />\r\n"; 
      lblTest.Text += "<hr />\r\n"; 
      if (doc.HasChildren) 
      { 
       Document[] childDocs = Document.GetChildrenForTree(doc.Id); 
       displayDocs(childDocs); //error occurs here 
      } 
     } 
    } 
} 

Answer 1

难道文档.GetChildrenForTree（doc.Id）方法返回null？