docs: private Certificate[] getCertificates(File container, String entry)
          throws IOException {
          if (container.isDirectory()) {
              return null;
          }
          JarFile jarFile = (JarFile) jarFiles.get(container);
          if (jarFile == null) {
              return null;
          }
          JarEntry ent = jarFile.getJarEntry(entry);
          return ent == null ? null : ent.getCertificates();
      }