I created a new job and tried to add a description setter to the job.
This is the error during save of the configuration.
With this the description setter is useless.

java.lang.IllegalArgumentException
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at org.kohsuke.stapler.RequestImpl.invokeConstructor(RequestImpl.java:391)
at org.kohsuke.stapler.RequestImpl.bindJSON(RequestImpl.java:344)
at hudson.plugins.descriptionsetter.DescriptionSetterPublisher$DescriptorImpl.newInstance(DescriptionSetterPublisher.java:192)
at hudson.plugins.descriptionsetter.DescriptionSetterPublisher$DescriptorImpl.newInstance(DescriptionSetterPublisher.java:171)
at hudson.util.DescribableList.rebuild(DescribableList.java:139)
at hudson.model.Project.submit(Project.java:201)
at hudson.model.FreeStyleProject.submit(FreeStyleProject.java:97)
at hudson.model.Job.doConfigSubmit(Job.java:968)
at hudson.model.AbstractProject.doConfigSubmit(AbstractProject.java:519)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:185)
at org.kohsuke.stapler.Function.bindAndInvoke(Function.java:101)
at org.kohsuke.stapler.Function.bindAndInvokeAndServeResponse(Function.java:54)
at org.kohsuke.stapler.MetaClass$1.doDispatch(MetaClass.java:74)
at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:30)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:492)
at org.kohsuke.stapler.MetaClass$6.doDispatch(MetaClass.java:180)
at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:30)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:492)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:408)
at org.kohsuke.stapler.Stapler.service(Stapler.java:117)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:45)
at winstone.ServletConfiguration.execute(ServletConfiguration.java:249)
at winstone.RequestDispatcher.forward(RequestDispatcher.java:335)
at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:378)
at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:94)
at hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:86)
at winstone.FilterConfiguration.execute(FilterConfiguration.java:195)
at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:368)
at hudson.security.csrf.CrumbFilter.doFilter(CrumbFilter.java:47)
at winstone.FilterConfiguration.execute(FilterConfiguration.java:195)
at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:368)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:84)
at hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:76)
at hudson.security.HudsonFilter.doFilter(HudsonFilter.java:164)
at winstone.FilterConfiguration.execute(FilterConfiguration.java:195)
at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:368)
at winstone.RequestDispatcher.forward(RequestDispatcher.java:333)
at winstone.RequestHandlerThread.processRequest(RequestHandlerThread.java:244)
at winstone.RequestHandlerThread.run(RequestHandlerThread.java:150)
at java.lang.Thread.run(Unknown Source)