Missing Implementation-Build manifest entry on Sitemap Forge Plugin

When deploying the cms the Sitemap forge plugin produces some warnings:

Build number not valid, not storing it on initialize item 'forge.onehippo.org.sitemap-hst-components-sitemap-component'. Is Implementation-Build manifest entry missing?
Build number not valid, not storing it on initialize item 'forge.onehippo.org.sitemap-hst-components-sitemap-based-on-hst-sitemap-component'. Is Implementation-Build manifest entry missing?
Build number not valid, not storing it on initialize item 'forge.onehippo.org.sitemap-hst-components-news-sitemap-component'. Is Implementation-Build manifest entry missing?
Build number not valid, not storing it on initialize item 'forge.onehippo.org.sitemap-hst-components-sitemap-index-component'. Is Implementation-Build manifest entry missing?
Build number not valid, not storing it on initialize item 'forge.onehippo.org.sitemap-hst-components-sitemap-template'. Is Implementation-Build manifest entry missing?
Build number not valid, not storing it on initialize item 'forge.onehippo.org.sitemap-hst-components-sitemap-sitemap-entry'. Is Implementation-Build manifest entry missing?

The MANIFEST.MF misses the Implementation-Build property. By adding the following to the <build> section of the project pom of the Sitemap forge plugin the Implementation-Build property will be filled by the build number generated by the maven buildnumber plugin:

<plugins>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>buildnumber-maven-plugin</artifactId>
<version>1.2</version>
<executions>
<execution>
<phase>validate</phase>
<goals>
<goal>create</goal>
</goals>
</execution>
</executions>
<configuration>
<doCheck>false</doCheck>
<doUpdate>false</doUpdate>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>2.1</version>
<configuration>
<archive>
<manifest>
<addDefaultImplementationEntries>true</addDefaultImplementationEntries>
</manifest>
<manifestEntries>
<Implementation-Build>${buildNumber}</Implementation-Build>
</manifestEntries>
</archive>
</configuration>
</plugin>
</plugins>