You have the same problem as Balaji. You are pointing to a resource that is not on the jar's classpath, which results in a NPE. You have :
@Override
public String getSmallIconPath() {
return "icons/coins.png";
}
But your icon file is at coins.png; there is no icons package.
Look at the Eclipse log; it should tell you precisely where the NPE is so you can see it's at:
Details: java.lang.NullPointerException
at java.util.zip.ZipFile.getInputStream(ZipFile.java:180)
at java.util.jar.JarFile.getInputStream(JarFile.java:385)
at org.activiti.designer.property.extension.CustomServiceTaskContextImpl.getSmallIconStream(CustomServiceTaskContextImpl.java:38)
Your small icon stream is null. I quote from the userguide:
"If you want to provide an icon, make sure it's in the src/main/resources package in your JAR and is about 16x16 pixels and a JPEG or PNG format. The path you supply is relative to that folder."