FIX Treat value not in SingleSelectField options as blank #2097

Job	Run time
CI / Context	1s
CI / Generate matrix	11s
CI / Check governance	1s
CI / 8.1 prf-low mysql57 phpunit framework-core	5m 19s
CI / 8.2 mariadb phpunit framework-core	5m 25s
CI / 8.3 mysql80 phpunit framework-core	6m 59s
CI / 8.3 mysql84 phpunit framework-core	6m 39s
CI / 8.1 prf-low mysql57 phpunit framework-orm	10m 49s
CI / 8.2 mariadb phpunit framework-orm	10m 27s
CI / 8.3 mysql80 phpunit framework-orm	11m 31s
CI / 8.3 mysql84 phpunit framework-orm	11m 27s
CI / 8.1 prf-low mysql57 phpunit cms	1m 36s
CI / 8.2 mariadb phpunit cms	1m 36s
CI / 8.3 mysql80 phpunit cms	1m 33s
CI / 8.3 mysql84 phpunit cms	1m 35s
CI / 8.1 mysql57 phplinting	2m 38s
CI / Dispatch tag patch release	0s
	1h 17m 47s

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