error 500 when clicking on book title

[richardh9935]

I'm using the front-end (public) view of my library.
When I click on a book author, the library shows me the author and associated books, as expected.
However, when I click on the title, either from the main view or the author view, the browser gives HTTP error 500. 
To see a better error message, in Joomla Global configuration, Server Settings, I changed "Error Reporting" to "Development", and did the same clicks as above.  Here is the error message:

Fatal error: Class 'JFolder' not found in /home/cactusac/public_html/dev/joomla30/components/com_abook/views/book/view.html.php on line 164

Although I can find that file on the server using Cpanel, I cannot find line 164.  It stops much before that.  Here is the code segment that I found that contains JFolder.

      $this->folderlist   = $this->get('FolderList');
      if ($this->item->docsfolder != ''){
         $this->docslist      = JFolder::files(JPATH_ROOT.DS.$this->item->docsfolder.DS, '', '', '', array('.svn', 'CVS','.DS_Store','__MACOSX', 'index.html'));


What are my options?
ie

Can I turn off the ability to click on the book title?
Can I amend the file named?
Should I create a folder called JFolder?
If so, where?

richard.

[federica]

Hi richardh9935,
which abook version are you using?

[richardh9935]

Component V 3.1.1, dated 2016-01-26


Fatal error: Class 'JFolder' not found in /home/cactusac/public_html/dev/joomla30/components/com_abook/views/book/view.html.php on line 164

[federica]

Check your database at table #_abbook, the column docslist must be empty or NULL

[richardh9935]

 

Using phpMyAdmin, I could not find the column "docslist" in table  _abbook, but I found "docsfolder".  This had many non-NULL values.  I changed all of them to NULL, using the MySQL UPDATE command, and now the database works perfectly.

Thanks.