SQL: CASTing passes instead of throwing an exception

[astefan]

SELECT (CAST('bla' AS DATE) IS NOT NULL)

yields

CAST('bla' AS DATE) IS NOT NULL
-------------------------------
true    

But running SELECT CAST('bla' AS DATE) throws an (expected) exception:

                "type": "sql_illegal_argument_exception",
                "reason": "cannot cast [bla] to [date]: Text 'bla' could not be parsed at index 0"

In reality, both cases should have thrown the sql_illegal_argument_exception. In the first case, though, bla is evaluated as not being null and the optimizer is already returning TRUE for IS NOT NULL.

[elasticmachine]

Pinging @elastic/es-search (:Search/SQL)

[matriv]

master : 671e07a
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