bug: props with optional getters should be validated

[timyates]

Previously in 3.x a class with optional getters was still validated.

This reproducer tests this case, and shows that it currently fails to validate.

If you remove the getter from the POGO, then the test passes.

This was discovered in building the hibernate-reactive guide where we have the following validated DTO:

https://github.com/micronaut-projects/micronaut-guides/blob/ab0bfb2c117de73b24aabbb9422ec58dadaebb8d/guides/micronaut-hibernate-reactive/java/src/main/java/example/micronaut/SortingAndOrderArguments.java

There's a reproducer here: #165