some refactoring

src/main/java/kieker/analysis/dev/OperationsDependency.java

@@ -40,17 +40,19 @@ public class OperationsDependency {
 
 	private void addRelation(final AggregatedOperationCall call) {
 
-		if (call.getParent() == null) {
+		AggregatedOperationCall parentCall = call.getParent();
+
+		if (parentCall == null) {
 			// TODO parent shouldn't be null. Create a class "EntryOperationCall".
 			return;
 		}
 
-		String key = call.getIdentifier() + ',' + call.getParent().getIdentifier();
+		String key = call.getIdentifier() + ',' + parentCall.getIdentifier();
 
 		if (!relations.containsKey(key)) {
 
 			AggregatedOperationCall callee = operations.get(call.getIdentifier());
-			AggregatedOperationCall caller = operations.get(call.getParent().getIdentifier());
+			AggregatedOperationCall caller = operations.get(parentCall.getIdentifier());
 
 			OperationsDependencyRelation relation = new OperationsDependencyRelation(callee, caller);
 			relations.put(key, relation);