In one of my regular sites I needed to use the content plugin in a custom module.  This works fine except if one needs to edit any Download from the front end. This is quite a common feature with several enabled users.  However clicking on the Edit 'pencil' gives the fault:

Error 0 Call to a member function get() on null
It is related to setting Prepare Content option in the custom module
 
This method is the standard way of using the content plugin in a module - see
 http://www.jdownloads.net/documentation-for-jd3-2/modules-plugins-v3-2/using-the-content-plugin-in-articles-and-modules
 

Colin
Joomla! 3.9.16 and  jD 3.2.66

Should be fixed in 3.2.67.