I have a jenkins installation that had gradle plugin version 2.12.1 installed and the system is also using the JCasC (Jenkins configuration-as-code) plugin.  I did the usual plugins upgrade and told Jenkins to restart after installing the updates.

Jenkins refused to start thereafter.  I got the error:

Oct 01 15:13:05 jenkins2.mydomain.com jenkins[120719]: 2024-10-01 20:13:05.682+0000 [id=30]        SEVERE        jenkins.InitReactorRunner$1#onTaskFailed: Failed ConfigurationAsCode.init

Oct 01 15:13:05 jenkins2.mydomain.com jenkins[120719]: io.jenkins.plugins.casc.UnknownAttributesException: injectionConfig: Invalid configuration elements for type: class hudson.plugins.gradle.injection.InjectionConfig : injectCcudExtension,injectMavenExtension.

Oct 01 15:13:05 jenkins2.mydomain.com jenkins[120719]: Available attributes : accessKeyCredentialId, allowUntrusted, ccudExtensionCustomCoordinates, ccudExtensionVersion, ccudPluginVersion, checkForBuildAgentErrors, enabled, enforceUrl, gradleCaptureTaskInputFiles, gradleInjectionDisabledNodes, gradleInjectionEnabledNodes, gradlePluginRepositoryCredentialId, gradlePluginRepositoryUrl, gradlePluginVersion, mavenCaptureGoalInputFiles, mavenExtensionCustomCoordinates, mavenExtensionRepositoryCredentialId, mavenExtensionRepositoryUrl, mavenExtensionVersion, mavenInjectionDisabledNodes, mavenInjectionEnabledNodes, server, shortLivedTokenExpiry, vcsRepositoryFilter

Oct 01 15:13:05 jenkins2.mydomain.com jenkins[120719]:         at io.jenkins.plugins.casc.BaseConfigurator.handleUnknown(BaseConfigurator.java:389)

My jenkins had this content in the file:
    /var/lib/jenkins/hudson.plugins.gradle.injection.InjectionConfig.xml

<?xml version='1.1' encoding='UTF-8'?>
<hudson.plugins.gradle.injection.InjectionConfig plugin="gradle@2.12.1">
  <enabled>false</enabled>
  <allowUntrusted>false</allowUntrusted>
  <gradleCaptureTaskInputFiles>true</gradleCaptureTaskInputFiles>
  <injectMavenExtension>false</injectMavenExtension>
  <injectCcudExtension>false</injectCcudExtension>
  <mavenCaptureGoalInputFiles>true</mavenCaptureGoalInputFiles>
  <enforceUrl>false</enforceUrl>
  <checkForBuildAgentErrors>false</checkForBuildAgentErrors>
  <parsedVcsRepositoryFilter>
    <vcsRepositoryFilter></vcsRepositoryFilter>
    <inclusion class="empty-list"/>
    <exclusion class="empty-list"/>
  </parsedVcsRepositoryFilter>
</hudson.plugins.gradle.injection.InjectionConfig>

and, sure enough, there are references to attributes injectCcudExtension and injectMavenExtension and the file indicates plugin="gradle@2.12.1".

I looked through the 2.12.1 source files and found .html files referencing these attributes, but those .html files were not present in 2.13.  So I assume dropping these attributes is intentional.

I reverted to the 2.12.1 jenkins plugin and jenkins would then start again.

I'm not sure if this is a bug with the plugin upgrade process, plugin backward compatibility, or user error.  Is there something I need to do when I upgrade Jenkins plugins to make sure any pre-existing .xml file for the plugin likewise gets updated? 

I don't use gradle myself and fairly new to JCasC.  Thanks