Running a Jenkinsfile without a tool version results in an unhelpful Groovy exception (Cannot get property 'method' on null object). Jenkins should detect this and give some clue as to what is wrong with the script. That can save lots of time for those who are not intimately familiar with the pipeline script syntax.

The problem is with the line that says

        maven

If you replace it with:

        maven 'system'

it all works fine.

Test case:

#!groovy
pipeline {
    agent none

    tools {
        maven
    }

    stages {
        stage('Initialize') {
            agent any
            steps {
                sh '''
                    echo "PATH = ${PATH}"
                '''
            }
        }
    }
}

The behavour is the same regardless of the tool; i.e. substituting 'maven' for 'jdk' or any other installed tool witout version results in the same exception:

 
java.lang.NullPointerException: Cannot get property 'method' on null object
at org.codehaus.groovy.runtime.NullObject.getProperty(NullObject.java:60)
at org.codehaus.groovy.runtime.InvokerHelper.getProperty(InvokerHelper.java:174)
at org.codehaus.groovy.runtime.callsite.PojoMetaClassGetPropertySite.callGetProperty(PojoMetaClassGetPropertySite.java:44)
at org.jenkinsci.plugins.pipeline.modeldefinition.parser.ModelParser$_parseTools_closure9.doCall(ModelParser.groovy:405)
at sun.reflect.GeneratedMethodAccessor642.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:294)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1022)
at groovy.lang.Closure.call(Closure.java:414)
at groovy.lang.Closure.call(Closure.java:430)
at org.codehaus.groovy.runtime.DefaultGroovyMethods.collect(DefaultGroovyMethods.java:3202)
at org.codehaus.groovy.runtime.DefaultGroovyMethods.collect(DefaultGroovyMethods.java:3172)
at org.codehaus.groovy.runtime.dgm$66.doMethodInvoke(Unknown Source)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1213)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1022)
at org.codehaus.groovy.runtime.callsite.PojoMetaClassSite.call(PojoMetaClassSite.java:47)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125)
at org.jenkinsci.plugins.pipeline.modeldefinition.parser.ModelParser.eachStatement(ModelParser.groovy:1191)
at sun.reflect.GeneratedMethodAccessor458.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.codehaus.groovy.runtime.callsite.PogoMetaMethodSite$PogoCachedMethodSiteNoUnwrapNoCoerce.invoke(PogoMetaMethodSite.java:210)
at org.codehaus.groovy.runtime.callsite.PogoMetaMethodSite.callCurrent(PogoMetaMethodSite.java:59)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:174)
at org.jenkinsci.plugins.pipeline.modeldefinition.parser.ModelParser.parseTools(ModelParser.groovy:398)
at sun.reflect.GeneratedMethodAccessor825.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:384)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1022)
at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.callCurrent(PogoMetaClassSite.java:69)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:166)
at org.jenkinsci.plugins.pipeline.modeldefinition.parser.ModelParser$_parse_closure5.doCall(ModelParser.groovy:167)
at sun.reflect.GeneratedMethodAccessor478.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:294)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1022)
at groovy.lang.Closure.call(Closure.java:414)
at groovy.lang.Closure.call(Closure.java:430)
at org.codehaus.groovy.runtime.DefaultGroovyMethods.collect(DefaultGroovyMethods.java:3202)
at org.codehaus.groovy.runtime.DefaultGroovyMethods.collect(DefaultGroovyMethods.java:3172)
at org.codehaus.groovy.runtime.dgm$66.doMethodInvoke(Unknown Source)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1213)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1022)
at org.codehaus.groovy.runtime.callsite.PojoMetaClassSite.call(PojoMetaClassSite.java:47)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125)
at org.jenkinsci.plugins.pipeline.modeldefinition.parser.ModelParser.eachStatement(ModelParser.groovy:1191)
at sun.reflect.GeneratedMethodAccessor458.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1213)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1022)
at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.callCurrent(PogoMetaClassSite.java:69)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:174)
at org.jenkinsci.plugins.pipeline.modeldefinition.parser.ModelParser.parse(ModelParser.groovy:140)
at sun.reflect.GeneratedMethodAccessor829.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1213)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1022)
at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.callCurrent(PogoMetaClassSite.java:69)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:166)
at org.jenkinsci.plugins.pipeline.modeldefinition.parser.ModelParser.parse(ModelParser.groovy:91)
at org.jenkinsci.plugins.pipeline.modeldefinition.parser.GroovyShellDecoratorImpl$1.call(GroovyShellDecoratorImpl.java:46)
at org.codehaus.groovy.control.CompilationUnit.applyToPrimaryClassNodes(CompilationUnit.java:1065)
Caused: BUG! exception in phase 'canonicalization' in source unit 'WorkflowScript' unexpected NullpointerException
at org.codehaus.groovy.control.CompilationUnit.applyToPrimaryClassNodes(CompilationUnit.java:1070)
at org.codehaus.groovy.control.CompilationUnit.doPhaseOperation(CompilationUnit.java:603)
at org.codehaus.groovy.control.CompilationUnit.processPhaseOperations(CompilationUnit.java:581)
at org.codehaus.groovy.control.CompilationUnit.compile(CompilationUnit.java:558)
at groovy.lang.GroovyClassLoader.doParseClass(GroovyClassLoader.java:298)
at groovy.lang.GroovyClassLoader.parseClass(GroovyClassLoader.java:268)
at groovy.lang.GroovyShell.parseClass(GroovyShell.java:688)
at groovy.lang.GroovyShell.parse(GroovyShell.java:700)
at org.jenkinsci.plugins.workflow.cps.CpsGroovyShell.doParse(CpsGroovyShell.java:129)
at org.jenkinsci.plugins.workflow.cps.CpsGroovyShell.reparse(CpsGroovyShell.java:123)
at org.jenkinsci.plugins.workflow.cps.CpsFlowExecution.parseScript(CpsFlowExecution.java:516)
at org.jenkinsci.plugins.workflow.cps.CpsFlowExecution.start(CpsFlowExecution.java:479)
at org.jenkinsci.plugins.workflow.job.WorkflowRun.run(WorkflowRun.java:252)
at hudson.model.ResourceController.execute(ResourceController.java:98)
at hudson.model.Executor.run(Executor.java:405)
Finished: FAILURE