Bug fix in explicit MDPs: actions added as 0.0 instead of null.

git-svn-id: https://www.prismmodelchecker.org/svn/prism/prism/trunk@3646 bbc10eb1-c90d-0410-af57-cb519fbb1720

prism/src/explicit/MDPSimple.java

@@ -376,7 +376,7 @@ public class MDPSimple extends ModelExplicit implements MDP, ModelSimple
 			int n = trans.get(s).size();
 			List<Object> list = new ArrayList<Object>(n);
 			for (int j = 0; j < n; j++) {
-				list.add(0.0);
+				list.add(null);
 			}
 			actions.set(s, list);
 		}