code: public HostKey getHostKey(Computer host) throws IOException {
          HostKey key = cache.get(host);
          if (null == key) {
              File hostKeyFile = getSshHostKeyFile(host.getNode());
              if (hostKeyFile.exists()) {
                  XmlFile xmlHostKeyFile = new XmlFile(hostKeyFile);
                  key = (HostKey) xmlHostKeyFile.read();
              } else {
                  key = null;
              }
              cache.put(host, key);
          }
          return key;
      }
docs: Retrieve the currently trusted host key for the requested computer, or null if
  no key is currently trusted.
  @param host the Computer to retrieve the key for.
  @return the currently trusted key for the requested host, or null if no key is trusted.
  @throws IOException if the host key can not be read from storage