Make RestOperations extensions parameters nullability consistent with Java API [SPR-16328]

[spring-projects-issues]

Sébastien Deleuze opened SPR-16328 and commented

In RestOperations extensions, nullability of parameters should be consistent with the Java API. It is currently not the case for requestEntity for example. Also potentially using null default parameters where that's possible could make sense.

---

Referenced from: commits d2616b7