The plantuml.jars which will be downloaded by Maven does not contain OpenIconics SVG graphics.
This seems to be a problem with PlantUMLs Maven build. If one builds PlantUML with Ant all the graphics are included but not when building with Maven.
Adding the follwing line in pom.xml should fix this problem:
<include>net/sourceforge/plantuml/version/favicon.png</include>
+ <include>net/sourceforge/plantuml/openiconic/data/*.svg</include>
</includes>
Regards,
Christoph