NullPointerException during GAE Java deployment via Maven (Unable to update app: null)

[Keith via StackOverflow]

I'm getting an exception that seems to happen intermittently, and only on some build machines. This is with GAE for Java v1.9.7.

I'm calling:

mvn -DskipTests=true -Dappengine.oauth2=false \
    -Dappengine.passin=true -Dappengine.email=x...@xxx.com \
    install appengine:update

(I'm passing in the password on stdin via piping in a Bash script.)

I see this in the logs:

Beginning interaction for module default...
Dec 17, 2014 1:16:20 PM com.google.appengine.tools.admin.AbstractServerConnection send1
WARNING: Error posting to URL: https://appengine.google.com/api/appversion/getresourcelimits?app_id=myappid&version=auto-master-2014-12-17&
401 Unauthorized
Must authenticate first.
This is try #0
Password for x...@xxx.com: 
java.lang.NullPointerException
Unable to update app: null
Please see the logs [/tmp/appcfg8165216295414974805.log] for further information.

And the exception is:

java.lang.NullPointerException
        at java.net.URLEncoder.encode(URLEncoder.java:205)
        at com.google.appengine.tools.admin.AbstractServerConnection.buildQuery(AbstractServerConnection.java:107)
        at com.google.appengine.tools.admin.ClientLoginServerConnection.getAuthToken(ClientLoginServerConnection.java:195)
        at com.google.appengine.tools.admin.ClientLoginServerConnection.authenticate(ClientLoginServerConnection.java:86)
        at com.google.appengine.tools.admin.ClientLoginServerConnection.doHandleSendErrors(ClientLoginServerConnection.java:120)
        at com.google.appengine.tools.admin.AbstractServerConnection.send1(AbstractServerConnection.java:305)
        at com.google.appengine.tools.admin.AbstractServerConnection.send(AbstractServerConnection.java:254)
        at com.google.appengine.tools.admin.AbstractServerConnection.post(AbstractServerConnection.java:233)
        at com.google.appengine.tools.admin.LoggingClientDeploySender.send(LoggingClientDeploySender.java:47)
        at com.google.appengine.tools.admin.ResourceLimits.remoteRequest(ResourceLimits.java:173)
        at com.google.appengine.tools.admin.ResourceLimits.request(ResourceLimits.java:139)
        at com.google.appengine.tools.admin.AppAdminImpl.doUpdate(AppAdminImpl.java:468)
        at com.google.appengine.tools.admin.AppAdminImpl.update(AppAdminImpl.java:55)
        at com.google.appengine.tools.admin.AppCfg$UpdateAction.execute(AppCfg.java:1361)
        at com.google.appengine.tools.admin.AppCfg.executeAction(AppCfg.java:332)
        at com.google.appengine.tools.admin.AppCfg.<init>(AppCfg.java:213)
        at com.google.appengine.tools.admin.AppCfg.<init>(AppCfg.java:124)
        at com.google.appengine.tools.admin.AppCfg.main(AppCfg.java:120)
        at com.google.appengine.appcfg.AbstractAppCfgMojo.executeAppCfgCommand(AbstractAppCfgMojo.java:250)
        at com.google.appengine.appcfg.Update.execute(Update.java:32)
        at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:133)
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:208)
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
        at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:108)
        at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:76)
        at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:51)
        at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:116)
        at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:361)
        at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:155)
        at org.apache.maven.cli.MavenCli.execute(MavenCli.java:584)
        at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:213)
        at org.apache.maven.cli.MavenCli.main(MavenCli.java:157)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:606)
        at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
        at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
        at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
        at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)

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http://stackoverflow.com/questions/27526694/nullpointerexception-during-gae-java-deployment-via-maven-unable-to-update-app