Matlab doc command not working: Error using doc>displayDocPage (line 171)

The doc command in my Matlab R2018B (relatively fresh) install on Windows 10 64bit is not working anymore.

When I type doc and some command, the following shows:

>> doc abs
Error using doc>displayDocPage (line 171)
Java exception occurred:
java.lang.NullPointerException

  at com.mathworks.help.helpui.DocRoot.buildUrl(DocRoot.java:197)

  at com.mathworks.help.helpui.DocRoot.buildUrl(DocRoot.java:186)

  at com.mathworks.help.helpui.DocRoot.buildDocSetItemUrl(DocRoot.java:59)

  at com.mathworks.mde.help.DocCommandHelpBrowserTask.getUrlToDisplay(DocCommandHelpBrowserTask.java:42)

  at com.mathworks.mde.help.JsHelpBrowser.doHelpBrowserTask(JsHelpBrowser.java:242)

  at com.mathworks.mde.help.JsHelpBrowser.doHelpBrowserTask(JsHelpBrowser.java:238)

  at com.mathworks.mde.help.JsHelpBrowser.showReferencePage(JsHelpBrowser.java:122)

  at com.mathworks.mlservices.MLHelpServices.showReferencePage(MLHelpServices.java:199)

Error in doc (line 125)
    if ~displayDocPage(possibleTopics) && ~showHelpwin(topic)

>>

And when I just call doc, an empty doc window pops up, and the following error shows in the command window:

>> doc
Exception in thread "AWT-EventQueue-0": java.lang.NullPointerException
  at com.mathworks.mlwidgets.help.DocConfigUrlBuilder.getUrlForDocConfig(DocConfigUrlBuilder.java:29)
  at com.mathworks.mlwidgets.help.LightweightHelpPanel.getNavigationUrl(LightweightHelpPanel.java:280)
  at com.mathworks.mlwidgets.help.LightweightHelpPanel.setCurrentLocation(LightweightHelpPanel.java:178)
  at com.mathworks.mde.help.JsHelpBrowserClient.setCurrentLocation(JsHelpBrowserClient.java:196)
  at com.mathworks.mde.help.JsHelpBrowserClient.showClient(JsHelpBrowserClient.java:234)
  at com.mathworks.mde.help.JsHelpBrowser$OpenInNewBrowser.openBrowser(JsHelpBrowser.java:345)
  at com.mathworks.mde.help.JsHelpBrowser$JsHelpBrowserRunnable.createAndShowBrowser(JsHelpBrowser.java:297)
  at com.mathworks.mde.help.JsHelpBrowser$JsHelpBrowserRunnable.run(JsHelpBrowser.java:292)
  at java.awt.event.InvocationEvent.dispatch(Unknown Source)
  at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
  at java.awt.EventQueue.access$500(Unknown Source)
  at java.awt.EventQueue$3.run(Unknown Source)
  at java.awt.EventQueue$3.run(Unknown Source)
  at java.security.AccessController.doPrivileged(Native Method)
  at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
  at java.awt.EventQueue.dispatchEvent(Unknown Source)
  at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
  at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
  at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
  at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
  at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
  at java.awt.EventDispatchThread.run(Unknown Source)
>>

The help function is working fine. How can I solve this problem?

[Walter Roberson]

Did you happen to see a message about being unable to access a particular http port?

Try turning off Windows Firewall and restarting MATLAB and trying again.

[rickert]

No I did not see any message relating to accessing a specific port. I just thought that the problem resolved itself, but apparently it has something to do with my VPN connection. When I am not connected to a VPN, doc works fine. But when I am connection to the VPN of my institution, doc shows these errors.

[rickert]

Turning off the firewall and restarting Windows did not resolve the issue (while connected to VPN)

[Akshay Khadse]

Since you are able to access the documentation without VPN, it seems to me that your institution has a firewall behind the VPN which might be blocking the connections. You could contact your network administrators to confirm the same and seek a resolution.