CpeGui: NullPointerException when choosing a Descriptor of Collection Reader

(as reported by Eric Riebling on the mailing list, but this has been bothering us for a long time also, and I just confirmed it with the exact same exception)

When running CPE GUI and a Collection Reader is already part of the
configuration, if you click "Browse.." to select a different Collection
Reader (or even the same Collection Reader), a null pointer exception is
thrown. This has been happening to me for years, and happens on both
Windows and Linux. The only work-around is to edit the CPE descriptor's raw
XML and paste in the proper XML for the Collection Reader you wish to
replace with.

Here is the stack trace:

java.lang.NullPointerException
at org.apache.uima.tools.cpm.CpmPanel.fileSelected(CpmPanel.java:1509)
at
org.apache.uima.tools.util.gui.FileSelector$1.actionPerformed
(FileSelector.java:141)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
at
javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at
javax.swing.plaf.basic.BasicButtonListener.mouseReleased
(BasicButtonListener.java:236)
at java.awt.Component.processMouseEvent(Component.java:6288)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
at java.awt.Component.processEvent(Component.java:6053)
at java.awt.Container.processEvent(Container.java:2041)
at java.awt.Component.dispatchEventImpl(Component.java:4651)
at java.awt.Container.dispatchEventImpl(Container.java:2099)
at java.awt.Component.dispatchEvent(Component.java:4481)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
at java.awt.Container.dispatchEventImpl(Container.java:2085)
at java.awt.Window.dispatchEventImpl(Window.java:2478)
at java.awt.Component.dispatchEvent(Component.java:4481)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:643)
at java.awt.EventQueue.access$000(EventQueue.java:84)
at java.awt.EventQueue$1.run(EventQueue.java:602)
at java.awt.EventQueue$1.run(EventQueue.java:600)
at java.security.AccessController.doPrivileged(Native Method)
at
java.security.AccessControlContext$1.doIntersectionPrivilege
(AccessControlContext.java:87)
at
java.security.AccessControlContext$1.doIntersectionPrivilege
(AccessControlContext.java:98)
at java.awt.EventQueue$2.run(EventQueue.java:616)
at java.awt.EventQueue$2.run(EventQueue.java:614)
at java.security.AccessController.doPrivileged(Native Method)
at
java.security.AccessControlContext$1.doIntersectionPrivilege
(AccessControlContext.java:87)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:613)
at
java.awt.EventDispatchThread.pumpOneEventForFilters
(EventDispatchThread.java:269)
at
java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at
java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)