docs: @CheckForNull
      private static File guessManifest(@Nonnull File parent) {
          File file = new File(parent, "MANIFEST.MF");
          if(!file.isFile()){
              file = new File(parent, "META-INF/MANIFEST.MF");
          }
          if(!file.isFile()){
              file = new File(parent, "../META-INF/MANIFEST.MF");
          }
          if(file.isFile()){
              return file;
          }
          return null;
      }