SET with flags XX GET return empty string if the stored key is not a string

[adiholden]

When running SET with flags XX GET we return empty string if the stored key is not a string expected behaviour: GET -- Return the old string stored at key, or nil if key did not exist. An error is returned and SET aborted if the value stored at key is not a string.

how to reproduce: lpush key x SET key value XX GET

return value: "" and we set value to key expected: error WRONGTYPE Operation against a key holding the wrong kind of value