8ee2d4e0_kasper_s_source__What_
[How?] Icons can be defined by providing PNG icon (32x32 pixels) with the same name as the transformer class, in the JAR file. In my case the transformer class was GroovySimpleTransformer.java, so I made an icon available at GroovySimpleTransformer.png. [What?] 
My transformer had only a default icon
kasper's source
What?