Catch some potential NPEs

src/main/java/com/gitblit/manager/RepositoryManager.java

@@ -1113,9 +1113,16 @@ public class RepositoryManager implements IRepositoryManager {
 			// find the root, cached
 			String key = getRepositoryKey(repository);
 			RepositoryModel model = repositoryListCache.get(key);
+			if (model == null) {
+				return null;
+			}
+
 			while (model.originRepository != null) {
 				String originKey = getRepositoryKey(model.originRepository);
 				model = repositoryListCache.get(originKey);
+				if (model == null) {
+					return null;
+				}
 			}
 			ForkModel root = getForkModelFromCache(model.name);
 			return root;

src/main/java/com/gitblit/wicket/pages/ForksPage.java

@@ -136,6 +136,9 @@ public class ForksPage extends RepositoryPage {
 
 	protected List<FlatFork> flatten(ForkModel node, int level) {
 		List<FlatFork> list = new ArrayList<FlatFork>();
+		if (node == null) {
+			return list;
+		}
 		list.add(new FlatFork(node.repository, level));
 		if (!node.isLeaf()) {
 			for (ForkModel fork : node.forks) {