AttributeError in update_weather_data() when earthtools.org is unreachable

The indicator-weather logo doesn"t appear in the taskbar but the process is still present.
Configuration is default one since I can't access any configuration menu. Using dconf-tool I changed Yahoo weather source to Weather.com (parameter 'W' instead of 'Y').

The log file report an error :

[Fetcher] 2013-07-05 22:21:39,877 - DEBUG - Traceback (most recent call last):
  File "/usr/bin/indicator-weather", line 2008, in get_new_weather_data
    weather = self.get_weather()
  File "/usr/bin/indicator-weather", line 2144, in get_weather
    self.current_location.update_weather_data(self.weather_source)
  File "/usr/bin/indicator-weather", line 654, in update_weather_data
    timezone(self.location_details['timezone id']),
  File "/usr/lib/python2.7/dist-packages/pytz/__init__.py", line 157, in timezone
    if zone.upper() == 'UTC':
AttributeError: 'NoneType' object has no attribute 'upper'

Configuration :
 ubunt:~$ sb_release -d
        Description: Ubuntu 12.04.2 LTS 64 bits

        indicator-weather : VERSION = "13.05.29 'Rainy 6'"

apt-cache policy indicator-weather
indicator-weather:
  Installé : 13.05.29
  Candidat : 13.05.29
 Table de version :
 *** 13.05.29 0
        500 http://ppa.launchpad.net/weather-indicator-team/ppa/ubuntu/ precise/main amd64 Packages
        100 /var/lib/dpkg/status
     11.11.28-0ubuntu1.3 0
        500 http://us.archive.ubuntu.com/ubuntu/ precise-updates/universe amd64 Packages
     11.11.28-0ubuntu1 0
        500 http://us.archive.ubuntu.com/ubuntu/ precise/universe amd64 Packages

Installation process :
sudo add-apt-repository ppa:weather-indicator-team/ppa
sudo add-apt-repository ppa:pywapi-devel/ppa
sudo apt-get update
sudo apt-get install indicator-weather