@staticmethod
def get_param(param_data, param_group, param_name):
    """
        Get param data for a given attribute.

        :param param_data: all param data from VOEvent file
        :param param_group: param group in VOEvent which holds param_name
        :param param_name: name of parameter to get value for
        :type param_data: orderedmultidict.orderedmultidict.omdict
        :type param_group: str
        :type param_name: str
        :returns: param value if defined in VOEvent, else None
        :rtype: str, float, int, NoneType
        """
    try:
        return param_data.get(param_group).get(param_name).get('value')
    except AttributeError:
        return None
