docs: private FileEntry evict() {
        if (configuration.maxEntries() > 0) {
           synchronized (entries) {
              if (entries.size() > configuration.maxEntries()) {
                 Iterator<FileEntry> it = entries.values().iterator();
                 FileEntry fe = it.next();
                 it.remove();
                 return fe;
              }
           }
        }
        return null;
     }