Remove nullpointers from graph printing

sdg-cli/src/main/java/es/upv/mist/slicing/cli/DOTAttributes.java

@@ -26,6 +26,8 @@ public class DOTAttributes {
     public Map<String, Attribute> build() {
         Map<String, Attribute> map = new HashMap<>();
         for (var entry : this.map.entrySet()) {
+            if (entry.getValue() == null)
+                continue;
             Optional<String> string = entry.getValue().stream().reduce((a, b) -> a + "," + b);
             string.ifPresent(s -> map.put(entry.getKey(), createAttribute(s)));
         }

sdg-cli/src/main/java/es/upv/mist/slicing/cli/PDGLog.java

 package es.upv.mist.slicing.cli;
 
 import es.upv.mist.slicing.arcs.Arc;
-import es.upv.mist.slicing.arcs.pdg.ConditionalControlDependencyArc;
-import es.upv.mist.slicing.arcs.pdg.FlowDependencyArc;
-import es.upv.mist.slicing.arcs.pdg.ObjectFlowDependencyArc;
-import es.upv.mist.slicing.arcs.pdg.StructuralArc;
+import es.upv.mist.slicing.arcs.pdg.*;
 import es.upv.mist.slicing.arcs.sdg.InterproceduralArc;
 import es.upv.mist.slicing.graphs.pdg.PDG;
 
@@ -47,11 +44,14 @@ public class PDGLog extends GraphLog<PDG> {
 
     public static DOTAttributes pdgEdgeAttributes(Arc arc) {
         DOTAttributes res = new DOTAttributes();
-        res.set("label", arc.getLabel());
+        if (arc.getLabel() != null)
+            res.set("label", arc.getLabel());
         if (arc.isDataDependencyArc()
                 || arc instanceof FlowDependencyArc
                 || arc instanceof ObjectFlowDependencyArc)
             res.set("color", "red");
+        if (arc instanceof TotalDefinitionDependenceArc)
+            res.set("color", "pink");
         if (arc instanceof StructuralArc)
             res.add("style", "dashed");
         if (arc.isObjectFlow() && !(arc instanceof InterproceduralArc))