feat: make default value optional for ValueSignal #8602

Job	Run time
Build Java and TypeScript for other tasks	3m 0s
Check style	2m 10s
Gradle tests (ubuntu-latest)	3m 58s
Test Java	3m 22s
Gradle tests (windows-latest)	7m 16s
ITs (ubuntu-latest, group-1)	5m 10s
ITs (ubuntu-latest, group-2)	4m 27s
Test TypeScript	2m 31s
ITs (ubuntu-latest, some)	5m 10s
Tests Summary	3s
	37m 7s

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