Fixes AASXPackageManager handling aasx packages without files

Change-Id: I07d59eb8f341137a5ee06fa7806b7a48418a7a55
Signed-off-by: Daniel Espen <Daniel.Espen@iese.fraunhofer.de>
diff --git a/components/basys.components/basyx.components.docker/basyx.components.AASServer/src/main/java/org/eclipse/basyx/components/aas/aasx/AASXPackageManager.java b/components/basys.components/basyx.components.docker/basyx.components.AASServer/src/main/java/org/eclipse/basyx/components/aas/aasx/AASXPackageManager.java
index 7cfba6f..f2f534e 100644
--- a/components/basys.components/basyx.components.docker/basyx.components.AASServer/src/main/java/org/eclipse/basyx/components/aas/aasx/AASXPackageManager.java
+++ b/components/basys.components/basyx.components.docker/basyx.components.AASServer/src/main/java/org/eclipse/basyx/components/aas/aasx/AASXPackageManager.java
@@ -351,6 +351,10 @@
 			throws ParserConfigurationException, SAXException, IOException {
 		List<String> files = new ArrayList<>();
 
+		if (insRelFile == null) {
+			return files;
+		}
+
 		// create the XML document parser
 		DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
 		DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();