report failed merge with default strategy as such

src/de/uni_passau/fim/seibt/gitwrapper/repo/DefaultMergeStrategy.java

@@ -23,6 +23,10 @@ public class DefaultMergeStrategy implements MergeStrategy {
     @Override
     public Optional<Status> merge(Reference left, Reference right) {
         Optional<ProcessExecutor.ExecRes> mergeBase = repo.getGit().exec(repo.getDir(), "merge", "-n", "-q", right.getId());
+        if (mergeBase.isPresent() && mergeBase.get().failed()) {
+            // merge failed, and we don't want to know the state of the repo at the parent
+            return Optional.empty();
+        }
         return mergeBase.flatMap(res -> repo.getStatus());
     }