$error_message not defined before use

The $error_message variable is used in google_weather_show function.
But it has no value assigned before it's used in the following fragments of code:

if (!is_array($cv)) {
    watchdog('google weather', "Required cURL for download information about weather forecast from Google.", array(), WATCHDOG_ERROR);
    return $error_message;
  }

    return theme('google_weather_block', $content);
  }
  else {
    return $error_message;
  }  

This applies to both 6.1.4 and dev versions.