Revisit PropertyResolver Kotlin extensions [SPR-16883]

[spring-issuemaster]

Sébastien Deleuze opened SPR-16883 and commented

Currently the get operator extension for PropertyResolver used to access for example on Environnement is calling getRequiredProperty which prevents to use Kotlin null safety to get default value like val name = env["name"] ?: "default".

This issue intend to use getProperty instead of getRequiredProperty to achieve this behavior. This is a breaking change but I think this is worth doing it since use case of nullable return value + fallback seems to be very common based on Kotlin developer feedback.

This issue also introduce getProperty<Foo>(...) and getRequiredProperty<Foo>(...) Kotlin extensions.

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Referenced from: commits a7a29a8