Annotations for Nonnull, CheckForNull, and several others were proposed
for Java as part of dormant Java specification request JSR-305. The
proposal never became a part of standard Java.

Jenkins plugins should switch from using JSR-305 annotations to use
Spotbugs annotations that provide the same semantics.

The [mailing list discussion](https://groups.google.com/g/jenkinsci-dev/c/uE1wwtVi1W0/m/gLxdEJmlBQAJ)
from James Nord describes the affected annotations and why they should
be replaced with annotations that are actively maintained.

The ["Improve a plugin" tutorial](https://www.jenkins.io/doc/developer/tutorial-improve/replace-jsr-305-annotations/)
provides instructions to perform this change.

An [OpenRewrite recipe](https://docs.openrewrite.org/recipes/jenkins/javaxannotationstospotbugs)
is also available and is even better than the tutorial.

Confirmed that automated tests pass on Linux with Java 21.

https://github.com/jenkinsci/plugin-pom/releases/tag/plugin-4.82

Blue Ocean enhancements have stopped.  In the future, Blue Ocean will
be removed from ci.jenkins.io.  Better to prepare for that removal now.

https://www.jenkins.io/doc/book/blueocean/ says:

Blue Ocean status

Blue Ocean will not receive further functionality updates. Blue Ocean
will continue to provide easy-to-use Pipeline visualization, but it
will not be enhanced further. It will only receive selective updates
for significant security issues or functional defects.

Alternative options for Pipeline visualization, such as the Pipeline:
Stage View and Pipeline Graph View plugins, are available and offer some
of the same functionality. While not complete replacements for Blue Ocean,
contributions are encouraged from the community for continued development
of these plugins.

The Pipeline syntax snippet generator assists users as they define
Pipeline steps with their arguments. It is the preferred tool for Jenkins
Pipeline creation, as it provides online help for the Pipeline steps
available in your Jenkins controller. It uses the plugins installed
on your Jenkins controller to generate the Pipeline syntax. Refer to
the Pipeline steps reference page for information on all available
Pipeline steps.

… fix-jsr-305