JDD: Check for NULL ptr in Ref/Deref

Normally, we should catch the construction of JDDNodes with NULL pointers
beforehand, but for robustness we make sure that we do not call Cudd_Ref
and Cudd_Deref for a NULL DdNode*, as that leads to SIGSEGV crashes.


git-svn-id: https://www.prismmodelchecker.org/svn/prism/prism/trunk@10473 bbc10eb1-c90d-0410-af57-cb519fbb1720

prism/src/jdd/JDD.java

@@ -265,9 +265,17 @@ public class JDD
 	 */
 	public static void Ref(JDDNode dd)
 	{
+		long ptr = dd.ptr();
+		// For robustness, catch NULL pointer
+		// In general, this should not happen,
+		// as constructing a JDDNode with NULL
+		// pointer should not happen...
+		if (ptr == 0) {
+			throw new CuddOutOfMemoryException();
+		}
 		if (DebugJDD.debugEnabled)
 			DebugJDD.increment(dd);
-		DD_Ref(dd.ptr());
+		DD_Ref(ptr);
 	}
 	
 	/**
@@ -276,9 +284,17 @@ public class JDD
 	 */
 	public static void Deref(JDDNode dd)
 	{
+		long ptr = dd.ptr();
+		// For robustness, catch NULL pointer
+		// In general, this should not happen,
+		// as constructing a JDDNode with NULL
+		// pointer should not happen...
+		if (ptr == 0) {
+			throw new CuddOutOfMemoryException();
+		}
 		if (DebugJDD.debugEnabled)
 			DebugJDD.decrement(dd);
-		DD_Deref(dd.ptr());
+		DD_Deref(ptr);
 	}
 
 	/**