How to solve this error :Exception in thread "AWT-EventQueue-0": java.lang.​NullPointe​rException​?

I get following error in matlab:

Exception in thread "AWT-EventQueue-0": java.lang.NullPointerException

at com.mathworks.help.helpui.DocRoot.buildUrl(DocRoot.java:216)

at com.mathworks.help.helpui.DocRoot.buildDocPageUrl(DocRoot.java:44)

at com.mathworks.mlwidgets.help.CSHelpTopicMap.mapIdToUrl(CSHelpTopicMap.java:244)

at com.mathworks.mlwidgets.help.CSHelpTopicMap.mapID(CSHelpTopicMap.java:234)

at com.mathworks.mlwidgets.text.mcode.MatlabDocUtils.getMapID(MatlabDocUtils.java:89)

at com.mathworks.mlwidgets.text.mcode.MatlabDocUtils.idHasExtendedHelp(MatlabDocUtils.java:84)

at com.mathworks.mlwidgets.text.mcode.MatlabDocUtils.mlintTagHasExtendedHelp(MatlabDocUtils.java:100)

at com.mathworks.mlwidgets.text.mcode.MatlabDocUtils.access$200(MatlabDocUtils.java:17)

at com.mathworks.mlwidgets.text.mcode.MatlabDocUtils$CodeAnalyzerDocHelper.hasExtendedHelp(MatlabDocUtils.java:148)

at com.mathworks.widgets.text.mcode.analyzer.CodeAnalyzerMessageModel$CodeAnalyzerMessage.hasExtendedInformation(CodeAnalyzerMessageModel.java:177)

at com.mathworks.widgets.text.layer.EditorTip.makeButtonPanel(EditorTip.java:402)

at com.mathworks.widgets.text.layer.EditorTip.makeSingleMessageRow(EditorTip.java:377)

at com.mathworks.widgets.text.layer.EditorTip.addShortMessageComponentsToPanel(EditorTip.java:257)

at com.mathworks.widgets.text.layer.EditorTip.makeWholeTipComponent(EditorTip.java:244)

at com.mathworks.widgets.text.layer.EditorTip.makeWholeTipComponentWithoutExtendedMessage(EditorTip.java:213)

at com.mathworks.widgets.text.layer.EditorTip.setupBalloonTip(EditorTip.java:199)

at com.mathworks.widgets.text.layer.EditorTip.show(EditorTip.java:504)

at com.mathworks.widgets.text.MWToolTipSupport.makeAndShowTip(MWToolTipSupport.java:351)

at com.mathworks.widgets.text.MWToolTipSupport.makeTip(MWToolTipSupport.java:253)

at com.mathworks.widgets.text.MWToolTipSupport.makeTip(MWToolTipSupport.java:216)

at com.mathworks.widgets.text.MWToolTipSupport.makeTipAtMouse(MWToolTipSupport.java:185)

at com.mathworks.widgets.text.MWKit$MWBuildToolTipAction.actionPerformed(MWKit.java:1507)

at com.mathworks.mde.editor.EditorMKit$EditorBuildToolTipAction.actionPerformed(EditorMKit.java:163)

at org.netbeans.editor.BaseAction.actionPerformed(BaseAction.java:259)

at org.netbeans.editor.ext.ToolTipSupport.updateToolTip(ToolTipSupport.java:413)

at org.netbeans.editor.ext.ToolTipContext$1.updateToolTip(ToolTipContext.java:17)

at org.netbeans.editor.ext.ToolTipSupport.setToolTipVisible(ToolTipSupport.java:449)

at org.netbeans.editor.ext.ToolTipSupport.setToolTipVisible(ToolTipSupport.java:429)

at org.netbeans.editor.ext.ToolTipSupport.actionPerformed(ToolTipSupport.java:758)

at org.netbeans.editor.WeakTimerListener.actionPerformed(WeakTimerListener.java:63)

at javax.swing.Timer.fireActionPerformed(Timer.java:313)

at javax.swing.Timer$DoPostEvent.run(Timer.java:245)

at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)

at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)

at java.awt.EventQueue.access$500(EventQueue.java:97)

at java.awt.EventQueue$3.run(EventQueue.java:709)

at java.awt.EventQueue$3.run(EventQueue.java:703)

at java.security.AccessController.doPrivileged(Native Method)

at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)

at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)

at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205)

at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)

at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)

at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)

at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)

at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)