hasFile now returns an optional.

src/de/uni_passau/fim/gitwrapper/Reference.java

@@ -133,10 +133,10 @@ public abstract class Reference {
      * @param file The file to check the {@link Commit} for existence.
      * @return {@code True} if the {@link Commit} contains the file, {@code False} otherwise.
      */
-    public boolean hasFile(Path file) {
+    public Optional<Boolean> hasFile(Path file) {
         Optional<ProcessExecutor.ExecRes> result = git.exec(repo.getDir(), "cat-file",
                 "-e", id + ":" + file);
-        return result.get().succeeded();
+        return result.map(ProcessExecutor.ExecRes::succeeded);
     }
 
     @Override