[Bug]: NullPointer Exception with Nested `AGENT` config

[quincy-codametrix]

Jenkins Version

2.414.1

JTE Version

2.5.3

Bug Description

There is a NullPointerException thrown when trying to load a pipeline config with a nested AGENT keyword. The workaround we're using is just renaming the AGENT keyword at the lowest level, I know there are some differences between groovy and how the template engine loads variables, but if nested values of the same key aren't supported I would have expected a pipeline configuration error thrown by the plugin instead of a null pointer?

We only noticed this when using nested pipeline configs.
We load our configs and libraries using the SCM option.

Relevant log output

java.lang.NullPointerException
	at org.codehaus.groovy.runtime.metaclass.MetaClassRegistryImpl.getMetaClass(MetaClassRegistryImpl.java:281)
	at org.codehaus.groovy.runtime.InvokerHelper.getMetaClass(InvokerHelper.java:901)
	at org.codehaus.groovy.runtime.InvokerHelper$getMetaClass.call(Unknown Source)
	at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:47)
	at org.codehaus.groovy.runtime.InvokerHelper$getMetaClass.call(Unknown Source)
	at org.boozallen.plugins.jte.init.governance.config.dsl.PipelineConfigurationObject$_clear_prop_closure6.doCall(PipelineConfigurationObject.groovy:130)
	at jdk.internal.reflect.GeneratedMethodAccessor711795.invoke(Unknown Source)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.base/java.lang.reflect.Method.invoke(Unknown Source)
	at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:98)
	at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
	at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:264)
	at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1034)
	at groovy.lang.Closure.call(Closure.java:420)
	at org.codehaus.groovy.runtime.DefaultGroovyMethods.inject(DefaultGroovyMethods.java:5518)
	at org.codehaus.groovy.runtime.DefaultGroovyMethods.inject(DefaultGroovyMethods.java:5459)
	at org.codehaus.groovy.runtime.dgm$339.invoke(Unknown Source)
	at org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite$PojoMetaMethodSiteNoUnwrapNoCoerce.invoke(PojoMetaMethodSite.java:274)
	at org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite.call(PojoMetaMethodSite.java:56)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:136)
	at org.boozallen.plugins.jte.init.governance.config.dsl.PipelineConfigurationObject.clear_prop(PipelineConfigurationObject.groovy:129)
	at jdk.internal.reflect.GeneratedMethodAccessor712491.invoke(Unknown Source)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.base/java.lang.reflect.Method.invoke(Unknown Source)
	at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:98)
	at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
	at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:352)
	at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1034)
	at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.callCurrent(PogoMetaClassSite.java:68)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:177)
	at org.boozallen.plugins.jte.init.governance.config.dsl.PipelineConfigurationObject$_plus_closure1.doCall(PipelineConfigurationObject.groovy:77)
	at jdk.internal.reflect.GeneratedMethodAccessor710841.invoke(Unknown Source)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.base/java.lang.reflect.Method.invoke(Unknown Source)
	at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:98)
	at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
	at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:264)
	at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1034)
	at groovy.lang.Closure.call(Closure.java:420)
	at groovy.lang.Closure.call(Closure.java:436)
	at org.codehaus.groovy.runtime.DefaultGroovyMethods.each(DefaultGroovyMethods.java:2125)
	at org.codehaus.groovy.runtime.DefaultGroovyMethods.each(DefaultGroovyMethods.java:2110)
	at org.codehaus.groovy.runtime.DefaultGroovyMethods.each(DefaultGroovyMethods.java:2163)
	at org.codehaus.groovy.runtime.dgm$165.invoke(Unknown Source)
	at org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite$PojoMetaMethodSiteNoUnwrapNoCoerce.invoke(PojoMetaMethodSite.java:274)
	at org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite.call(PojoMetaMethodSite.java:56)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:128)
	at org.boozallen.plugins.jte.init.governance.config.dsl.PipelineConfigurationObject.plus(PipelineConfigurationObject.groovy:75)
	at org.boozallen.plugins.jte.init.governance.config.dsl.PipelineConfigurationObject$plus.call(Unknown Source)
	at org.boozallen.plugins.jte.init.PipelineConfigurationAggregator$_aggregate_closure1.doCall(PipelineConfigurationAggregator.groovy:51)
	at jdk.internal.reflect.GeneratedMethodAccessor711794.invoke(Unknown Source)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.base/java.lang.reflect.Method.invoke(Unknown Source)
	at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:98)
	at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
	at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:264)
	at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1034)
	at groovy.lang.Closure.call(Closure.java:420)
	at groovy.lang.Closure.call(Closure.java:436)
	at org.codehaus.groovy.runtime.DefaultGroovyMethods.each(DefaultGroovyMethods.java:2125)
	at org.codehaus.groovy.runtime.DefaultGroovyMethods.each(DefaultGroovyMethods.java:2110)
	at org.codehaus.groovy.runtime.DefaultGroovyMethods.each(DefaultGroovyMethods.java:2151)
	at org.codehaus.groovy.runtime.dgm$163.invoke(Unknown Source)
	at org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite$PojoMetaMethodSiteNoUnwrapNoCoerce.invoke(PojoMetaMethodSite.java:274)
	at org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite.call(PojoMetaMethodSite.java:56)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:128)
	at org.boozallen.plugins.jte.init.PipelineConfigurationAggregator.aggregate(PipelineConfigurationAggregator.groovy:48)
	at org.boozallen.plugins.jte.init.PipelineConfigurationAggregator$aggregate$0.call(Unknown Source)
	at org.boozallen.plugins.jte.job.TemplateFlowDefinition.create(TemplateFlowDefinition.groovy:77)
	at org.jenkinsci.plugins.workflow.job.WorkflowRun.run(WorkflowRun.java:311)
	at hudson.model.ResourceController.execute(ResourceController.java:101)
	at hudson.model.Executor.run(Executor.java:442)

Steps to Reproduce

Setup a pipeline config on the main branch of a jenkins templates repository:

...
@merge keywords {
  AGENT {
    RESOURCES {
      @override AGENT = '4GB'
      @override BUILD = '8GB'
    }
  }
}
...

Setup a "testing" pipeline config on another branch:

...
@merge keywords {
  AGENT {
    RESOURCES {
      @override AGENT = '4GB'
      @override BUILD = '8GB'
    }
  }
}
...

Configure Jenkins to globally load the main pipeline config.
Configure your job to load the testing pipeline config.
After starting the job the error should appear when trying to load the test branch pipeline config file.