@NotNull
  @Convert(PluginPsiClassConverter.class)
  @ExtendClass(allowEmpty = true)
  GenericDomValue<PsiClass> getHeadlessImplementationClass();
@NotNull
  @Convert(PluginPsiClassConverter.class)
  @ExtendClass(allowEmpty = true)
  GenericDomValue<PsiClass> getHeadlessImplementationClass()