Description

A content author can submit changes in the Rich Text Editor (RTE) field several times in a short period of time. Such actions might lead to one or more of the following symptoms.

• The loss of the changes.
• The following error in the RTE field and in the log records:
  

  [NullReferenceException: Object reference not set to an instance of an object.]
     System.Collections.Specialized.NameObjectCollectionBase.BaseRemove(String name) +130
     System.Web.SessionState.SessionStateItemCollection.Remove(String name) +96
     Sitecore.Web.WebUtil.RemoveSessionValue(String key) +109
     Sitecore.Shell.Controls.RADEditor.Preview.GetText() +54
     Sitecore.Shell.Controls.RADEditor.Preview.OnLoad(EventArgs e) +80
     System.Web.UI.Control.LoadRecursive() +153
     System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +4087

• Application crash with the following error in the log records:
  

  ERROR Unhandled exception detected. The ASP.NET worker process will be terminated.
  Exception: System.NullReferenceException
  Message: Object reference not set to an instance of an object.
  Source: System.Web
  at System.Web.SessionState.SessionStateItemCollection.get_Item(Int32 index)
  at System.Web.Util.AspCompatApplicationStep.AnyStaObjectsInSessionState(HttpSessionState session)
  at System.Web.HttpApplicationFactory.FireSessionOnEnd(HttpSessionState session, Object eventSource, EventArgs eventArgs)
  at System.Web.SessionState.SessionOnEndTargetWorkItem.RaiseOnEndCallback()
  at System.Web.Util.WorkItem.CallCallbackWithAssert(WorkItemCallback callback)
  at System.Web.Util.WorkItem.OnQueueUserWorkItemCompletion(Object state)

Technical details:

The issue occurs if the SessionStateBehavior is set to ReadOnly. Such behavior enables parallel processing of requests triggered by the same user. ReadOnly SessionStateBehavior does not prevent changes to a user's session. If two requests make concurrent changes to the same session then the session collection (not thread-safe by design) might become corrupted.

Solution

To resolve the issue, ensure that the ReadOnly SessionStateBehavior is not used. This can be done by considering one of the following options:

• Upgrade Sitecore XP instance to Sitecore XP 10.1.0 or later.
• If you do not use Experience Optimization (Content Testing) functionality, set ContentTesting.AutomaticContentTesting.Enabled to false by creating a configuration patch file in the [your_website]\App_Config\Include\zzz folder, as shown in the following:
  

  <?xml version="1.0" encoding="utf-8" ?>
  <configuration xmlns:patch="http://www.sitecore.net/xmlconfig/" xmlns:set="http://www.sitecore.net/xmlconfig/set/">
    <sitecore>
      <settings>
        <setting name="ContentTesting.AutomaticContentTesting.Enabled" set:value="false" />
      </settings>
    </sitecore>
  </configuration>

• If you use Experience Optimization, delete the processor <processor type="Sitecore.ContentTesting.Pipelines.HttpRequest.SetReadOnlySessionStateForScreenshot, Sitecore.ContentTesting> by creating a configuration patch file in the [your_website]\App_Config\Include\zzz folder, as shown in the following:
  

  <configuration xmlns:patch="http://www.sitecore.net/xmlconfig/" xmlns:set="http://www.sitecore.net/xmlconfig/set/">
      <sitecore>
          <pipelines>
              <httpRequestBegin>
                  <processor type="Sitecore.ContentTesting.Pipelines.HttpRequest.SetReadOnlySessionStateForScreenshot, Sitecore.ContentTesting">
                      <patch:delete />
                  </processor>
              </httpRequestBegin>
          </pipelines>
      </sitecore>
  </configuration>

  Note: Deleting this processor does not affect the application performance or functionality.