@Override
  public @Nullable String getHeaderField(String name) {
    try {
      connect();
    } catch (IOException e) {
      return null;
    }

    // no header should have more than one value
    return Iterables.getFirst(headers.get(Ascii.toLowerCase(name)), null);
  }
{@code URLConnection} implementation.

@author Colin Decker
jimfs/src/main/java/com/google/common/jimfs/PathURLConnection.java