fixed NPE

src/main/java/it/unibz/inf/isochrone/config/ConfigDataset.java

@@ -329,7 +329,8 @@ public class ConfigDataset {
 			// find resources on disk and add to available ones
 			URI r = null;
 			try {
-				r = cLoader.getResource("/").toURI();
+				final URL resource = cLoader.getResource("/");
+				r = resource == null ? null : resource.toURI();
 			} catch (final URISyntaxException e1) {
 				LOGGER.warn("Datasets directory URI could not be created. There might be no configured datasets available!");
 			}