Cannot upload: POM does not validate

I've got a pretty straightforward upload process, but it won't upload because the POM apparently won't validate. However, it seems valid to me, and it's generated pretty directly. I've attached the POM and the relevant files from the build directory.

FAILURE: Build failed with an exception.

• Where:
  Build file '/Users/robert/wkdir/ashlar/runtime/build.gradle'

• What went wrong:
  Execution failed for task ':runtime:uploadArchives'.
  Cause: Could not publish configurations [configuration ':runtime:archives'].

• Try:
  Run with -S option to get the full (very verbose) stacktrace.

• Exception is:
  org.gradle.api.tasks.LocationAwareTaskExecutionException: Build file '/Users/robert/wkdir/ashlar/runtime/build.gradle'
  Execution failed for task ':runtime:uploadArchives'.
  at org.gradle.api.internal.tasks.DefaultTaskExecuter.executeActions(DefaultTaskExecuter.java:63)
  at org.gradle.api.internal.tasks.DefaultTaskExecuter.execute(DefaultTaskExecuter.java:41)
  at org.gradle.api.internal.project.taskfactory.PostExecutionAnalysisTaskExecuter.execute(PostExecutionAnalysisTaskExecuter.java:32)
  at org.gradle.api.internal.project.taskfactory.ExecutionShortCircuitTaskExecuter.execute(ExecutionShortCircuitTaskExecuter.java:50)
  at org.gradle.api.internal.tasks.SkipTaskExecuter.doExecute(SkipTaskExecuter.java:57)
  at org.gradle.api.internal.tasks.SkipTaskExecuter.execute(SkipTaskExecuter.java:35)
  at org.gradle.api.internal.tasks.ExecuteAtMostOnceTaskExecuter.execute(ExecuteAtMostOnceTaskExecuter.java:32)
  at org.gradle.api.internal.AbstractTask.execute(AbstractTask.java:231)
  at org.gradle.execution.DefaultTaskGraphExecuter.executeTask(DefaultTaskGraphExecuter.java:167)
  at org.gradle.execution.DefaultTaskGraphExecuter.doExecute(DefaultTaskGraphExecuter.java:160)
  at org.gradle.execution.DefaultTaskGraphExecuter.execute(DefaultTaskGraphExecuter.java:78)
  at org.gradle.execution.TaskNameResolvingBuildExecuter.execute(TaskNameResolvingBuildExecuter.java:161)
  at org.gradle.execution.DelegatingBuildExecuter.execute(DelegatingBuildExecuter.java:54)
  at org.gradle.initialization.DefaultGradleLauncher.doBuildStages(DefaultGradleLauncher.java:153)
  at org.gradle.initialization.DefaultGradleLauncher.doBuild(DefaultGradleLauncher.java:107)
  at org.gradle.initialization.DefaultGradleLauncher.run(DefaultGradleLauncher.java:75)
  at org.gradle.launcher.Main.execute(Main.java:93)
  at org.gradle.launcher.Main.main(Main.java:42)
  at org.gradle.launcher.GradleMain.main(GradleMain.java:49)
  Caused by: org.gradle.api.GradleException: Could not publish configurations [configuration ':runtime:archives'].
  at org.gradle.api.internal.artifacts.ivyservice.ErrorHandlingIvyService.publish(ErrorHandlingIvyService.java:44)
  at org.gradle.api.internal.artifacts.configurations.DefaultConfiguration.publish(DefaultConfiguration.java:211)
  at org.gradle.api.tasks.Upload.upload(Upload.java:57)
  at org.gradle.api.internal.BeanDynamicObject.invokeMethod(BeanDynamicObject.java:158)
  at org.gradle.api.internal.CompositeDynamicObject.invokeMethod(CompositeDynamicObject.java:93)
  at org.gradle.api.tasks.Upload_Decorated.invokeMethod(Unknown Source)
  at org.gradle.util.ReflectionUtil.invoke(ReflectionUtil.groovy:23)
  at org.gradle.api.internal.project.taskfactory.AnnotationProcessingTaskFactory$2.execute(AnnotationProcessingTaskFactory.java:131)
  at org.gradle.api.internal.project.taskfactory.AnnotationProcessingTaskFactory$2.execute(AnnotationProcessingTaskFactory.java:129)
  at org.gradle.api.internal.tasks.DefaultTaskExecuter.executeActions(DefaultTaskExecuter.java:55)
  ... 18 common frames omitted
  Caused by: org.apache.tools.ant.BuildException: Unable to initialize POM pom-default.xml: Failed to validate POM for project ashlar:ashlar-runtime at /Users/robert/wkdir/ashlar/runtime/build/poms/pom-default.xml
  at org.apache.maven.artifact.ant.Pom.initialiseMavenProject(Pom.java:211)
  at org.apache.maven.artifact.ant.AbstractArtifactTask.initializePom(AbstractArtifactTask.java:528)
  at org.apache.maven.artifact.ant.InstallDeployTaskSupport.initializePom(InstallDeployTaskSupport.java:60)
  at org.apache.maven.artifact.ant.DeployTask.doExecute(DeployTask.java:100)
  at org.gradle.api.internal.artifacts.publish.maven.deploy.CustomDeployTask.doExecute(CustomDeployTask.java:42)
  at org.apache.maven.artifact.ant.AbstractArtifactTask.execute(AbstractArtifactTask.java:721)
  at org.gradle.api.internal.artifacts.publish.maven.deploy.AbstractMavenResolver.execute(AbstractMavenResolver.java:185)
  at org.gradle.api.internal.artifacts.publish.maven.deploy.AbstractMavenResolver.commitPublishTransaction(AbstractMavenResolver.java:176)
  at org.apache.ivy.core.publish.PublishEngine.publish(PublishEngine.java:262)
  at org.gradle.api.internal.artifacts.ivyservice.DefaultIvyDependencyPublisher.publish(DefaultIvyDependencyPublisher.java:54)
  at org.gradle.api.internal.artifacts.ivyservice.DefaultIvyService.publish(DefaultIvyService.java:144)
  at org.gradle.api.internal.artifacts.ivyservice.ShortcircuitEmptyConfigsIvyService.publish(ShortcircuitEmptyConfigsIvyService.java:61)
  at org.gradle.api.internal.artifacts.ivyservice.ErrorHandlingIvyService.publish(ErrorHandlingIvyService.java:42)
  ... 27 common frames omitted
  Caused by: org.apache.maven.project.InvalidProjectModelException: Failed to validate POM for project ashlar:ashlar-runtime at /Users/robert/wkdir/ashlar/runtime/build/poms/pom-default.xml
  at org.apache.maven.project.DefaultMavenProjectBuilder.processProjectLogic(DefaultMavenProjectBuilder.java:1077)
  at org.apache.maven.project.DefaultMavenProjectBuilder.buildInternal(DefaultMavenProjectBuilder.java:880)
  at org.apache.maven.project.DefaultMavenProjectBuilder.buildFromSourceFileInternal(DefaultMavenProjectBuilder.java:508)
  at org.apache.maven.project.DefaultMavenProjectBuilder.build(DefaultMavenProjectBuilder.java:200)
  at org.apache.maven.artifact.ant.Pom.initialiseMavenProject(Pom.java:207)
  ... 39 common frames omitted