When config.xml is present in an Eclipse Linked folder (not in a symbolic link), then attempting to add or remove plugins (and possibly other operations on config.xml) fails with a spurious NullPointerException (without a stacktrace).

This pretty much means that the Hybrid Mobile application project with a linked folder for 'www' is in a read-only state for plugin addition/removal. If any plugin should be added or removed, the linked folder must be dropped, converted to an ordinary folder (or symbolic link), and then re-created after modifications.

To verify
1. create a new project
2. copy www folder to an alternate location
3. remove www folder
4.add www folder from alternate location as a linked folder (New Folder > Advanced> Link to alternate location)
5. add cordova plugins to the project. [Check they are added]