java.lang.NullPointerException when trying to Debug
The target definition file may not be correctly formed. This is the xml file file in the same directory as your .project file.
In this file check that the value of board id element is in quotes as such as < board id ="custom">
Found from this user post
http://www.openstm32.org/tiki-view_forum_thread.php?comments_parentId=875
This is an issue in the stm32cube mx v4.9.0 and 4.10.0 and apparently has been reported to ST.