Fixes AAS Environment Serialization (#866)

Author: FriedJannik

basyx.aasenvironment/basyx.aasenvironment-core/src/main/java/org/eclipse/digitaltwin/basyx/aasenvironment/base/DefaultAASEnvironment.java

@@ -414,6 +414,9 @@ private static String getHashedFilePath(String filePath) throws NoSuchAlgorithmE
 	}
 
 	private static boolean isURL(String path) {
+		if(path == null || path.isEmpty()) {
+			return false;
+		}
 		return path.startsWith("http");
 	}
 }