java.lang.NullPointerException
	at org.eclipse.emf.compare.diff.DefaultDiffEngine.computeContainmentDifferences(DefaultDiffEngine.java:328)
	at org.eclipse.emf.compare.diff.DefaultDiffEngine.computeDifferences(DefaultDiffEngine.java:757)
	at org.eclipse.emf.compare.diff.DefaultDiffEngine.internalCheckForDifferences(DefaultDiffEngine.java:180)
	at org.eclipse.emf.compare.diff.DefaultDiffEngine.internalCheckForDifferences(DefaultDiffEngine.java:191)
	at org.eclipse.emf.compare.diff.DefaultDiffEngine.internalCheckForDifferences(DefaultDiffEngine.java:191)
	at org.eclipse.emf.compare.diff.DefaultDiffEngine.checkForDifferences(DefaultDiffEngine.java:156)
	at org.eclipse.emf.compare.diff.DefaultDiffEngine.diff(DefaultDiffEngine.java:129)
	at org.eclipse.emf.compare.EMFCompare.compare(EMFCompare.java:240)
	at org.eclipse.emf.compare.EMFCompare.compare(EMFCompare.java:182)