JCasC plugin does not apply all of the 'Nomad plugin' related entries from jenkins.yaml although these entries are listed in the JSON schema (<jenkins_url>/configuration-as-code/schema).
In the result the Nomad plugin is not well configured and java.lang.NullPointerException are caused in the plugin's code when a slave is set up (e.g. at org.jenkinsci.plugins.nomad.NomadApi.buildDriverConfig(NomadApi.java:142)).

The missing entries in my case are

• org.jenkinsci.plugins.nomad.NomadCloud.jenkinsTunnel
• org.jenkinsci.plugins.nomad.NomadSlaveTemplate.remoteFs
• org.jenkinsci.plugins.nomad.NomadSlaveTemplate.prefixCmd

If I add them manually to the Jenkins' config.xml the setup of a Nomad slave succeeds.

Beside that the export of the configuration causes an StackOverflowError:

FAILED TO EXPORT
org.jenkinsci.plugins.nomad.NomadSlaveTemplate#cloud: java.lang.StackOverflowError
at java.util.Collections$UnmodifiableCollection$1.<init>(Collections.java:1039)
at java.util.Collections$UnmodifiableCollection.iterator(Collections.java:1038)
...
Caused: java.lang.reflect.InvocationTargetException
at sun.reflect.GeneratedConstructorAccessor133.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at io.jenkins.plugins.casc.impl.configurators.DataBoundConfigurator.describe(DataBoundConfigurator.java:265)
at io.jenkins.plugins.casc.Attribute.describe(Attribute.java:202)
at io.jenkins.plugins.casc.BaseConfigurator.compare(BaseConfigurator.java:391)
at io.jenkins.plugins.casc.impl.configurators.DataBoundConfigurator.describe(DataBoundConfigurator.java:268)
at io.jenkins.plugins.casc.Attribute.describe(Attribute.java:198)

This seems to be caused by recursive loop: The cloud definition contains an arry of node templates. Each template definition contains a cloud object which references the cloud object which this template list belongs to.