Alpha2 Metadata Error on Start

[Marvin Addison]

> Apologies for the simple suggestion, but if you revert your changes to
> attribute-filter.xml and attribute-resolver.xml does the problem still
> occur ?

It's a good suggestion and I should have tried it straight away. I was
busy most of yesterday trying Scott's suggestion of using
relying-party-legacy.xml, and and ran into another mess of
configuration issues so I aborted.

I just reverted all the conf/* changes and the error disappears on
startup. So it's something in one of my attribute configs. I copied
attribute-resolver.xml back into conf/ and I get a different error but
same root cause, invalid constraint on null ID:

09:46:54.575 - ERROR
[net.shibboleth.utilities.java.support.service.AbstractReloadableService:171]
- Service 'shibboleth.MetadataResolverService': initial load failed {}
net.shibboleth.utilities.java.support.service.ServiceException:
org.springframework.beans.factory.BeanCreationException: Error
creating bean with name 'ShibbolethMetadata': Cannot create inner bean
'(inner bean)#158c156' of type
[org.opensaml.saml.metadata.resolver.impl.ChainingMetadataResolver]
while setting constructor argument; nested exception is
org.springframework.beans.factory.BeanCreationException: Error
creating bean with name '(inner bean)#158c156': Cannot create inner
bean '(inner bean)#4bb3e41e' of type
[org.opensaml.saml.metadata.resolver.impl.FilesystemMetadataResolver]
while setting bean property 'resolvers' with key [0]; nested exception
is org.springframework.beans.factory.BeanCreationException: Error
creating bean with name '(inner bean)#4bb3e41e': Invocation of init
method failed; nested exception is
net.shibboleth.utilities.java.support.component.ComponentInitializationException:
Error refreshing metadata during init
...
Caused by: net.shibboleth.utilities.java.support.logic.ConstraintViolationExcept
ion: Component ID can not be null or empty
        at net.shibboleth.utilities.java.support.logic.Constraint.isNotNull(Cons
traint.java:210) ~[java-support-4.0.0.jar:na]
        at net.shibboleth.utilities.java.support.component.AbstractIdentifiedIni
tializableComponent.setId(AbstractIdentifiedInitializableComponent.java:53) ~[ja
va-support-4.0.0.jar:na]
        at net.shibboleth.utilities.java.support.component.AbstractIdentifiableI
nitializableComponent.setId(AbstractIdentifiableInitializableComponent.java:30)
~[java-support-4.0.0.jar:na]
        at net.shibboleth.idp.saml.attribute.encoding.impl.SAML2ScopedStringAttr
ibuteEncoder.populateAttributeMapper(SAML2ScopedStringAttributeEncoder.java:181)
 ~[idp-saml-impl-3.0.0-alpha2.jar:na]

Based on the last entry of the stack trace, I can imagine that one of
my attribute encoder definitions is bad, but the original error
message was misleading by mentioning metadata. Anyway, I believe I
have a lead on tracking down the root problem.

Thanks,
M