The manual suggests defining GERRIT_REFSPEC to ref/heads/master to allow building from Jenkings without gerrit triggering.

However, it's not working because of something else:

groovy.lang.MissingPropertyException: No such property: GERRIT_CHANGE_NUMBER for class: groovy.lang.Binding
at groovy.lang.Binding.getVariable(Binding.java:63)
at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SandboxInterceptor.onGetProperty(SandboxInterceptor.java:271)
at org.kohsuke.groovy.sandbox.impl.Checker$7.call(Checker.java:353)
at org.kohsuke.groovy.sandbox.impl.Checker.checkedGetProperty(Checker.java:357)
at org.kohsuke.groovy.sandbox.impl.Checker.checkedGetProperty(Checker.java:333)
at org.kohsuke.groovy.sandbox.impl.Checker.checkedGetProperty(Checker.java:333)
at com.cloudbees.groovy.cps.sandbox.SandboxInvoker.getProperty(SandboxInvoker.java:29)
at com.cloudbees.groovy.cps.impl.PropertyAccessBlock.rawGet(PropertyAccessBlock.java:20)
at WorkflowScript.run(WorkflowScript:13)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.delegateAndExecute(ModelInterpreter.groovy:137)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.executeSingleStage(ModelInterpreter.groovy:661)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.catchRequiredContextForNode(ModelInterpreter.groovy:395)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.catchRequiredContextForNode(ModelInterpreter.groovy:393)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.executeSingleStage(ModelInterpreter.groovy:660)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.evaluateStage(ModelInterpreter.groovy:288)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.toolsBlock(ModelInterpreter.groovy:544)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.toolsBlock(ModelInterpreter.groovy:543)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.evaluateStage(ModelInterpreter.groovy:276)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.withEnvBlock(ModelInterpreter.groovy:443)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.withEnvBlock(ModelInterpreter.groovy:442)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.evaluateStage(ModelInterpreter.groovy:275)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.withCredentialsBlock(ModelInterpreter.groovy:481)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.withCredentialsBlock(ModelInterpreter.groovy:480)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.evaluateStage(ModelInterpreter.groovy:274)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.inDeclarativeAgent(ModelInterpreter.groovy:586)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.inDeclarativeAgent(ModelInterpreter.groovy:585)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.evaluateStage(ModelInterpreter.groovy:272)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.stageInput(ModelInterpreter.groovy:356)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.stageInput(ModelInterpreter.groovy:355)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.evaluateStage(ModelInterpreter.groovy:261)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.inWrappers(ModelInterpreter.groovy:613)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.inWrappers(ModelInterpreter.groovy:612)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.evaluateStage(ModelInterpreter.groovy:259)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.withEnvBlock(ModelInterpreter.groovy:443)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.withEnvBlock(ModelInterpreter.groovy:442)
at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.evaluateStage(ModelInterpreter.groovy:254)
at __cps.transform__(Native Method)
at com.cloudbees.groovy.cps.impl.PropertyishBlock$ContinuationImpl.get(PropertyishBlock.java:74)
at com.cloudbees.groovy.cps.LValueBlock$GetAdapter.receive(LValueBlock.java:30)
at com.cloudbees.groovy.cps.impl.PropertyishBlock$ContinuationImpl.fixName(PropertyishBlock.java:66)
at jdk.internal.reflect.GeneratedMethodAccessor253.invoke(Unknown Source)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at com.cloudbees.groovy.cps.impl.ContinuationPtr$ContinuationImpl.receive(ContinuationPtr.java:72)
at com.cloudbees.groovy.cps.impl.ConstantBlock.eval(ConstantBlock.java:21)
at com.cloudbees.groovy.cps.Next.step(Next.java:83)
at com.cloudbees.groovy.cps.Continuable$1.call(Continuable.java:174)
at com.cloudbees.groovy.cps.Continuable$1.call(Continuable.java:163)
at org.codehaus.groovy.runtime.GroovyCategorySupport$ThreadCategoryInfo.use(GroovyCategorySupport.java:129)
at org.codehaus.groovy.runtime.GroovyCategorySupport.use(GroovyCategorySupport.java:268)
at com.cloudbees.groovy.cps.Continuable.run0(Continuable.java:163)
at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.access$001(SandboxContinuable.java:18)
at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.run0(SandboxContinuable.java:51)
at org.jenkinsci.plugins.workflow.cps.CpsThread.runNextChunk(CpsThread.java:185)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.run(CpsThreadGroup.java:400)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.access$400(CpsThreadGroup.java:96)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:312)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:276)
at org.jenkinsci.plugins.workflow.cps.CpsVmExecutorService$2.call(CpsVmExecutorService.java:67)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at hudson.remoting.SingleLaneExecutorService$1.run(SingleLaneExecutorService.java:139)
at jenkins.util.ContextResettingExecutorService$1.run(ContextResettingExecutorService.java:28)
at jenkins.security.ImpersonatingExecutorService$1.run(ImpersonatingExecutorService.java:68)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:829)