Document Null Safety Support in Reference Documentation

Closes gh-1662

Author: snicoll

spring-ws-docs/src/docs/asciidoc/common.adoc

@@ -6,6 +6,18 @@
 This chapter explores the components that are shared between client- and server-side Spring-WS development.
 These interfaces and classes represent the building blocks of Spring-WS, so you need to understand what they do, even if you do not use them directly.
 
+[[web-service-null-safety]]
+== Null Safety
+Spring-WS is annotated with https://jspecify.dev/docs/start-here/[JSpecify] annotations to declare the nullability of its API.
+To learn more about JSpecify, its https://jspecify.dev/docs/user-guide/[user guide] is recommended reading.
+
+The primary goal of declaring the nullability of the API is to prevent a `NullPointerException` from being thrown at runtime.
+This is achieved through build-time checks that are available with both Java and Kotlin.
+Performing the checks with Java requires some tooling such as https://github.com/uber/NullAway[NullAway] or an IDE that supports JSpecify annotations such as IntelliJ IDEA.
+The checks are available automatically with Kotlin which translates the JSpecify annotations into Kotlin's null safety.
+
+To learn more about null safety with Spring, refer to the {spring-framework-docs}/core/null-safety.html[Spring Framework reference documentation].
+
 [[web-service-messages]]
 == Web Service Messages
 

spring-ws-docs/src/docs/asciidoc/index.adoc

@@ -10,7 +10,7 @@ Arjen Poutsma, Rick Evans, Tareq Abed Rabbo, Greg Turnquist, Jay Bryant, Corneil
 :docs-site: https://docs.spring.io
 :spring-framework-docs-root: {docs-site}/spring-framework/docs
 :spring-framework-api: {spring-framework-docs-root}/{spring-framework-version}/javadoc-api/org/springframework
-:spring-framework-docs: https://docs.spring.io/spring-framework/reference
+:spring-framework-docs: https://docs.spring.io/spring-framework/reference/7.0
 :spring-ws-docs-root: {docs-site}/spring-ws/docs
 :spring-ws-api: {spring-ws-docs-root}/{spring-ws-version}/api/org/springframework/ws