GH-10083 Add nullability docs and whats-new info

Fixes: #10083

* Update docs to be more concise

* Remove reference to blog
* Remove the words "Spring Integration"  from the body and title
* Remove the version from the link to SF's reference doc and verified that it works

* Make sure only one sentence per line in asciidocs

Author: cppwfs

src/reference/antora/modules/ROOT/pages/index.adoc

@@ -75,3 +75,4 @@ xref:testing.adoc[Testing support] :: Test utilities, Integration mocks and test
 xref:samples.adoc#samples-impl[Spring Integration Samples] :: The samples dedicated project
 xref:resources.adoc[Additional Resources] :: Other resources related to project
 xref:history.adoc[Change History] :: The changes made in the project over time
+xref:null-safety.adoc[Null Safety] :: Null safety build-time enforcement

src/reference/antora/modules/ROOT/pages/null-safety.adoc

@@ -0,0 +1,7 @@
+[[null-safety]]
+= Null Safety
+
+The codebase is annotated with JSpecify annotations to declare the nullability of its APIs, fields, and related type usages, following Spring Framework's efforts to add null safety to the platform.
+Reading Spring Framework's https://docs.spring.io/spring-framework/reference/core/null-safety.html#null-safety-guidelines-nullaway[Null-safety reference documentation] is highly recommended to get familiar with these annotations and their semantics.
+
+The primary goal of this null-safety arrangement is to prevent `NullPointerException` from being thrown at runtime through build-time checks and to use explicit nullability as a way to express the possible absence of a value.

src/reference/antora/modules/ROOT/pages/whats-new.adoc

@@ -62,4 +62,9 @@ See xref:mqtt.adoc[] for more information.
 
 The `AbstractInboundFileSynchronizer` now caches a filtered result of the `Session.list(remoteDirectory)` after slicing by the `maxFetchSize`.
 So, later synchronizations deal with the cache only by the `maxFetchSize` until the cache is exhausted.
-See xref:sftp/max-fetch.adoc[] for more information.
+See xref:sftp/max-fetch.adoc[] for more information.
+
+[[x7.0-null-safety]]
+=== Null Safety
+Updated the codebase to use JSpecify and NullAway, adding a comprehensive null safety implementation that uses `@NullMarked` annotations to default all types to non-null at the package level and `@Nullable` annotations to explicitly mark types that can be null.
+See xref:null-safety.adoc[] for more information.