code: public long getLastModified(String path) throws GetLastModifiedException {
          String hash;
          Content content;
  
          hash = hashCache.probe(path);
          if (hash != null) {
              content = contentCache.probe(hash);
              if (content != null) {
                  return content.lastModified;
              }
          }
          return -1;
      }
docs: /* @return -1 (i.e: unknown) when not cached; not computed