generateSitemap=true creates xdoc that fails to validate with validate=true

I configured my site plugin with generateSitemap=true and validate=true. When I do so I get the error below. I've attached the generated sitemap.xml file.

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-site-plugin:3.0-beta-3:site (default-s
ite) on project stack-concurrency-spring: Error during page generation: Error parsing 'D:\projects\s
tack-3.0\stack-build\concurrency-spring\target\generated-site\xdoc\sitemap.xml': line [-1] Error val
idating the model: Error:
[ERROR] Public ID: null
[ERROR] System ID: null
[ERROR] Line number: 1
[ERROR] Column number: 649
[ERROR] Message: cvc-complex-type.2.4.a: Invalid content was found starting with element 'ul'. One o
f '

' is expected.
[ERROR] -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.apache.maven.plug
ins:maven-site-plugin:3.0-beta-3:site (default-site) on project stack-concurrency-spring: Error duri
ng page generation
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:203)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:148)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:140)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBu
ilder.java:84)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBu
ilder.java:59)
at org.apache.maven.lifecycle.internal.LifecycleStarter.singleThreadedBuild(LifecycleStarter
.java:183)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:161)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:316)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:153)
at org.apache.maven.cli.MavenCli.execute(MavenCli.java:451)
at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:188)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:134)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:290)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:230)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:409)
at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:352)
Caused by: org.apache.maven.plugin.MojoExecutionException: Error during page generation
at org.apache.maven.plugins.site.SiteMojo.execute(SiteMojo.java:127)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.j
ava:107)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:195)
... 19 more
Caused by: org.apache.maven.doxia.siterenderer.RendererException: Error parsing 'D:\projects\stack-3
.0\stack-build\concurrency-spring\target\generated-site\xdoc\sitemap.xml': line [-1] Error validatin
g the model: Error:
Public ID: null
System ID: null
Line number: 1
Column number: 649
Message: cvc-complex-type.2.4.a: Invalid content was found starting with element 'ul'. One of '

' is expected.

at org.apache.maven.doxia.siterenderer.DefaultSiteRenderer.renderDocument(DefaultSiteRendere
r.java:418)
at org.apache.maven.doxia.siterenderer.DoxiaDocumentRenderer.renderDocument(DoxiaDocumentRen
derer.java:53)
at org.apache.maven.doxia.siterenderer.DefaultSiteRenderer.renderModule(DefaultSiteRenderer.
java:330)
at org.apache.maven.doxia.siterenderer.DefaultSiteRenderer.render(DefaultSiteRenderer.java:1
34)
at org.apache.maven.plugins.site.SiteMojo.renderLocale(SiteMojo.java:175)
at org.apache.maven.plugins.site.SiteMojo.execute(SiteMojo.java:122)
... 21 more
Caused by: org.apache.maven.doxia.parser.ParseException: Error validating the model: Error:
Public ID: null
System ID: null
Line number: 1
Column number: 649
Message: cvc-complex-type.2.4.a: Invalid content was found starting with element 'ul'. One of '

' is expected.

at org.apache.maven.doxia.util.XmlValidator.validate(XmlValidator.java:116)
at org.apache.maven.doxia.siterenderer.DefaultSiteRenderer.validate(DefaultSiteRenderer.java
:879)
at org.apache.maven.doxia.siterenderer.DefaultSiteRenderer.renderDocument(DefaultSiteRendere
r.java:399)
... 26 more
Caused by: org.xml.sax.SAXException: Error:
Public ID: null
System ID: null
Line number: 1
Column number: 649
Message: cvc-complex-type.2.4.a: Invalid content was found starting with element 'ul'. One of '

' is expected.

at org.apache.maven.doxia.util.XmlValidator$MessagesErrorHandler.processException(XmlValidat
or.java:264)
at org.apache.maven.doxia.util.XmlValidator$MessagesErrorHandler.error(XmlValidator.java:202
)
at org.apache.xerces.util.ErrorHandlerWrapper.error(Unknown Source)
at org.apache.xerces.impl.XMLErrorReporter.reportError(Unknown Source)
at org.apache.xerces.impl.XMLErrorReporter.reportError(Unknown Source)
at org.apache.xerces.impl.XMLErrorReporter.reportError(Unknown Source)
at org.apache.xerces.impl.xs.XMLSchemaValidator$XSIErrorReporter.reportError(Unknown Source)

at org.apache.xerces.impl.xs.XMLSchemaValidator.reportSchemaError(Unknown Source)
at org.apache.xerces.impl.xs.XMLSchemaValidator.handleStartElement(Unknown Source)
at org.apache.xerces.impl.xs.XMLSchemaValidator.startElement(Unknown Source)
at org.apache.xerces.impl.XMLNSDocumentScannerImpl.scanStartElement(Unknown Source)
at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl$FragmentContentDispatcher.dispatch(
Unknown Source)
at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)
at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source)
at org.apache.maven.doxia.util.XmlValidator.validate(XmlValidator.java:108)
... 28 more
[ERROR]
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles: