SQL: NPE with ORDER BY re-aliased reference from subquery

[bpintea]

Ordering by a reference which itself points to an alias defined in a subquery will lead to a NPE:
SELECT g AS h FROM ( SELECT gender AS g FROM test_emp) ORDER BY h
will generate:

    "type" : "null_pointer_exception",
    "reason" : "Cannot invoke \"org.elasticsearch.xpack.ql.expression.Expression.hashCode()\" because \"e\" is null"

and grouping by it will raise:

    "type" : "sql_illegal_argument_exception",
    "reason" : "Cannot GROUP BY g{r}#18308"

[elasticmachine]

Pinging @elastic/es-ql (Team:QL)