fixed printing bug

src/main/jastadd/clauses/expressions.jadd

@@ -9,7 +9,10 @@ aspect SignalExpressions {
 
     eq Root.printExp() {
         String result = "";
-        result += getExp().printExp();
+
+        if(getExp() != null){
+            result+=getExp().printExp();
+        }
         return result;
     }
 

src/main/java/de/tudresden/inf/st/pnml/Main.java

@@ -19,13 +19,13 @@ public class Main {
 
         String inputPath = (args.length > 0) ? args[0] : null;
 
-     //   if(inputPath == null){
-   //         logger.error("No model found on given input path.");
-    //        return;
-    //    }
+        if(inputPath == null){
+            logger.error("No model found on given input path.");
+            return;
+        }
 
-        List<PetriNet> petriNets = PnmlParser.parsePnml("src/main/nets/inputSignalNet.pnml");
-      //  List<PetriNet> petriNets = PnmlParser.parsePnml(inputPath);
+       // List<PetriNet> petriNets = PnmlParser.parsePnml("src/main/nets/jointTestNet1.pnml");
+        List<PetriNet> petriNets = PnmlParser.parsePnml(inputPath);
 
         List<List<PetriNet>> disconnectedPetriNets = new ArrayList<>();
        // petriNets.forEach(pn -> disconnectedPetriNets.add(GlobalToLocalNetsPostProcessor.disconnectNets(pn)));

src/main/nets/inputSignalNet.pnml

@@ -54,7 +54,7 @@
 
             <transition id="t1">
                 <toolspecific tool="de.tudresden.inf.st.pnml.distributedPN" version="0.1">
-                  <!--  <location>channel</location>
+                   <location>channel</location>
                     <subnet>channel</subnet>-->
                     <location>node-1</location>
                     <subnet>subnet-1</subnet>