NPE when register agent, ImporterAgent.register()

[dominikl]

QA 42457

java.lang.NullPointerException
	at org.openmicroscopy.shoola.agents.fsimporter.ImporterAgent.register(ImporterAgent.java:359)
	at org.openmicroscopy.shoola.agents.fsimporter.ImporterAgent.setContext(ImporterAgent.java:465)
	at org.openmicroscopy.shoola.env.Container.startService(Container.java:418)

[jburel]

Fixed in #484