After working for a while with the IDE + debugging the following exception is 
systematically populated on any project when clicking on a sour line to set or 
unset a breakpoint.

Stoping + restarting Netbeans does not fix the problem :

java.lang.NullPointerException
	at 
org.netbeans.modules.ant.debugger.breakpoints.BreakpointsReader.write
(BreakpointsReader.java:57)
	at org.netbeans.api.debugger.Properties$PropertiesImpl.setObject
(Properties.java:652)
	at org.netbeans.api.debugger.Properties$DelegatingProperties.setObject
(Properties.java:873)
	at org.netbeans.api.debugger.Properties$PropertiesImpl.setArray
(Properties.java:688)
	at org.netbeans.api.debugger.Properties$DelegatingProperties.setArray
(Properties.java:881)
	at 
org.netbeans.modules.ant.debugger.breakpoints.PersistenceManager.breakpointAdde
d(PersistenceManager.java:60)
	at org.netbeans.api.debugger.DebuggerManager.fireBreakpointCreated
(DebuggerManager.java:632)
	at org.netbeans.api.debugger.DebuggerManager.addBreakpoint
(DebuggerManager.java:433)
	at 
org.netbeans.modules.debugger.jpda.ui.actions.ToggleBreakpointActionProvider.do
Action(ToggleBreakpointActionProvider.java:113)
	at org.netbeans.spi.debugger.ActionsProvider$1.run
(ActionsProvider.java:77)
	at org.openide.util.Task.run(Task.java:207)
	at org.openide.util.RequestProcessor$Task.run
(RequestProcessor.java:469)
[catch] at org.openide.util.RequestProcessor$Processor.run
(RequestProcessor.java:870)