Default methods not allowed in PipelineOptions

Start in org.apache.beam.sdk.options.PipelineOptionsFactory.java, especially validateMethodsAreEitherBeanMethodOrKnownMethod and the predicates used to identify unknown methods. Reproduce the reported default-method case, then verify that default methods are accepted while non-bean, non-static, non-synthetic, and non-known methods still fail validation.

If I create a class that extends PipelineOptions and contains a default method, the PipelineOptionsFactory will throw an exception because all non-static, non-synthetic and non-known methods need to have a getter and a setter.

For example, these PipelineOptions

public interface MyOptions extends PipelineOptions {
  void setValue(String s);
  String getValue();


  default List<String> getValues() {
     return Arrays.asList(getValue().split(","));
   }
}

will throw an exception in org.apache.beam.sdk.options.PipelineOptionsFactory.java:

private static void validateMethodsAreEitherBeanMethodOrKnownMethod(
    Class<? extends PipelineOptions>
iface,
    Class<? extends PipelineOptions> klass,
    List<PropertyDescriptor> descriptors) {

...
//
Verify that no additional methods are on an interface that aren't a bean property.
// Because methods
can have multiple declarations, we do a name-based comparison
// here to prevent false positives.
SortedSet<Method>
unknownMethods = new TreeSet<>(MethodComparator.INSTANCE);
unknownMethods.addAll(
    Sets.filter(

       Sets.difference(Sets.newHashSet(iface.getMethods()), knownMethods),
        Predicates.and(

           NOT_SYNTHETIC_PREDICATE,
            input -> !knownMethodsNames.contains(input.getName()),

           NOT_STATIC_PREDICATE)));
checkArgument(
    unknownMethods.isEmpty(),
    "Methods %s
on [%s] do not conform to being bean properties.",
    FluentIterable.from(unknownMethods).transform(ReflectHelpers.METHOD_FORMATTER),

   iface.getName());
}

Having a NOT_DEFAULT_PREDICATE in addition to the other predicates would allow 

private static final Predicate<Method> NOT_DEFAULT_PREDICATE = input -> !input.isDefault();

Seems like it would do the trick.

Imported from Jira BEAM-8669. Original Jira may contain additional context.
Reported by: chrisstockton.