'Check if a given value is ``null``.
Criteria for this is based on values that shouldn\'t be included
in the Solr ``add`` request at all.'

def _is_null_value(self, value):

    if (value is None):
        return True
    if IS_PY3:
        if (isinstance(value, str) and (len(value) == 0)):
            return True
    elif (isinstance(value, basestring) and (len(value) == 0)):
        return True
    return False
