docs: def get_values(self, *args):
          """
          Gets environment variables values.
  
          Usage::
  
              >>> environment = Environment("HOME")
              >>> environment.get_values()
              {'HOME': u'/Users/JohnDoe'}
              >>> environment.get_values("USER")
              {'HOME': u'/Users/JohnDoe', 'USER': u'JohnDoe'}
  
          :param \*args: Additional variables names to retrieve values from.
          :type \*args: \*
          :return: Variables : Values.
          :rtype: dict
          """
  
          args and self.__add_variables(*args)
  
          LOGGER.debug("> Object environment variables: '{0}'.".format(
              ",".join((key for key in self.__variables if key))))
          LOGGER.debug("> Available system environment variables: '{0}'".format(os.environ.keys()))
  
          for variable in self.__variables:
              value = os.environ.get(variable, None)
              self.__variables[variable] = foundations.strings.to_string(value) if value else None
          return self.__variables