Allow loading GHStorage with a single CH preparation

Author: easbar

core/src/main/java/com/graphhopper/storage/GraphHopperStorage.java

@@ -282,12 +282,6 @@ private void checkIfConfiguredAndLoadedWeightingsCompatible() {
         String loadedStr = properties.get("graph.ch.profiles");
         List<String> loaded = parseList(loadedStr);
         List<CHProfile> configured = getCHProfiles();
-        // todo: not entirely sure here. when no ch is configured at all (neither edge nor node), but there are any
-        // ch graphs (edge or node) we throw an error ? previously we threw an error when no ch weighting was configured
-        // even though there was a ch graph.
-        if (configured.isEmpty() && !loaded.isEmpty()) {
-            throw new IllegalStateException("You loaded a CH graph, but you did not specify any CH weightings in prepare.ch.weightings");
-        }
         for (CHProfile chProfile : configured) {
             if (!loaded.contains(chProfile.toString())) {
                 throw new IllegalStateException("Configured CH profile: " + chProfile.toString() + " is not contained in loaded weightings for CH" + loadedStr + ".\n" +

core/src/test/java/com/graphhopper/storage/GraphHopperStorageCHTest.java

@@ -592,6 +592,13 @@ private void testLoadingWithLessWeightings_works(boolean edgeBased) {
         assertEquals(edgeBased ? 1 : 0, smallStorage.getCHProfiles(true).size());
         smallStorage.flush();
 
+        // now we create a new storage without any ch weightings, which should also be ok
+        GraphHopperStorage smallerStorage = createStorageWithWeightings();
+        smallerStorage.loadExisting();
+        assertEquals(0, smallerStorage.getCHProfiles(false).size());
+        assertEquals(0, smallerStorage.getCHProfiles(true).size());
+        smallerStorage.flush();
+
         // now we create yet another storage that uses both weightings again, which still works
         GraphHopperStorage fullStorage = createStorageWithWeightings(
                 "car|fastest|" + edgeOrNode,