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Why am I not able to use the installed help documentation properly after update in MATLAB 9.6 (R2019a)?

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Whenever searching any keywords in Help Documentation, there is only empty page by just showing loading image permanently with the following error message in the MATLAB command window.
Exception in thread "com.mathworks.mlwidgets.help.messages.HelpSystemMessageChannel Message Channel Thread": java.lang.NullPointerException
at com.mathworks.search.lucene.LuceneIndexUtils.indexContainsField(LuceneIndexUtils.java:75)
at com.mathworks.helpsearch.DocSearchEngineFactory.createAutoSearchEngine(DocSearchEngineFactory.java:50)
at com.mathworks.help.helpui.search.DocSearchHandler.doSearch(DocSearchHandler.java:59)
at com.mathworks.help.helpui.search.DocSearchHandler.doSearch(DocSearchHandler.java:52)
at com.mathworks.mlwidgets.help.messages.search.DocSearchMessageHandler.handleSearch(DocSearchMessageHandler.java:47)
at com.mathworks.mlwidgets.help.messages.search.DocSearchMessageHandler.handle(DocSearchMessageHandler.java:41)
at com.mathworks.mlwidgets.html.messages.BrowserMessageSubscriber$HelpMessageRunnable.run(BrowserMessageSubscriber.java:110)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
The above same issue is also occurred when typing "docsearch plot" at the MATLAB prompt.

Accepted Answer

MathWorks Support Team
MathWorks Support Team on 25 Mar 2020
Edited: MathWorks Support Team on 25 Mar 2020
There is a bug in MATLAB 9.6 (R2019a) in using both the following 2 settings after installed any update in R2019a which was installed with "English" for "Windows display language".
1. Set "Language" as Languages with a non-latin character set like "Korean" in Preferences > Help
2. Set "Documentation Location" as "Installed locally" in Preferences > Help
To work around this issue, change the “Documentation Location” to “mathworks.com” from “Installed locally” in Preference > Help in MATLAB.
Or, go to http://kr.mathworks.com/help website from your browser and then change the country selection to like “한국 (한국어)” at the bottom.

More Answers (3)

Anuj Nagar
Anuj Nagar on 29 Jan 2020
I can't see anything like language preference in my dialogue box, I am getting the same Error.
Exception in thread "com.mathworks.mlwidgets.help.messages.HelpSystemMessageChannel Message Channel Thread": java.lang.NullPointerException
at com.mathworks.search.lucene.LuceneIndexUtils.indexContainsField(LuceneIndexUtils.java:75)
at com.mathworks.helpsearch.DocSearchEngineFactory.createAutoSearchEngine(DocSearchEngineFactory.java:50)
at com.mathworks.help.helpui.search.DocSearchHandler.doSearch(DocSearchHandler.java:59)
at com.mathworks.help.helpui.search.DocSearchHandler.doSearch(DocSearchHandler.java:52)
at com.mathworks.mlwidgets.help.messages.search.DocSearchMessageHandler.handleSearch(DocSearchMessageHandler.java:47)
at com.mathworks.mlwidgets.help.messages.search.DocSearchMessageHandler.handle(DocSearchMessageHandler.java:41)
at com.mathworks.mlwidgets.html.messages.BrowserMessageSubscriber$HelpMessageRunnable.run(BrowserMessageSubscriber.java:110)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)


Patrik Forssén
Patrik Forssén on 22 Jan 2021
This error is encountered if you add paths to MATLAB that contains a “html” folder, e.g., a third-party toolbox. MATLAB then seems to assume that the “html” folder is help and tries to build a search index in a folder “helpsearch-v3” (R2020a). However, the built index might be corrupt and will then break the help search function and make it throw this Java error. MATLAB should of course check the built index, or at least handle the error in the help search system, but it doesn’t.
The fix is to just remove the “html” and “helpsearch” folders from the MATLAB path.
MATLAB’s help system seems to be very unstable. If it stops working another fix is to exit MATLAB and delete everything in the folder that is returned if you type “prefdir” at the MATLAB command prompt. On Windows typically something like,
C:\Users\<UserName>\AppData\Roaming\MathWorks\MATLAB\<Release>
Note that this will also delete any set preferences.
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