code: public Installable getInstallable() throws IOException {
          for (Installable i : ((DescriptorImpl<?>)getDescriptor()).getInstallables())
              if(id.equals(i.id))
                  return i;
          return null;
      }
docs: Gets the {@link Installable} identified by {@link #id}.
  
  @return null if no such ID is found.