fix by Vincent

org.fortiss.tooling.kernel/trunk/src/org/fortiss/tooling/kernel/internal/ConstraintService.java

@@ -163,6 +163,9 @@ public final class ConstraintService implements IIntrospectiveKernelService, ICo
 	/** {@inheritDoc} */
 	@Override
 	public boolean isUpToDate(ConstraintInstance ci) {
+		if(ci == null) {
+			throw new NullPointerException();
+		}
 		for(IConstrained c : ci.getConstraineds()) {
 			BigInteger computeCheckSum = computeCheckSum(c, ci);
 			EMap<String, BigInteger> checksumMap = c.getChecksumsPerConstraintName();