SAML Metadata spec
http://docs.oasis-open.org/security/saml/v2.0/saml-metadata-2.0-os.pdf
states in 2.3.1: "A SAML metadata instance describes either a single entity or multiple entities. In the former case, the root element MUST be <EntityDescriptor>. In the latter case, the root element MUST be <EntitiesDescriptor>.
PicketLink parsing with root element EntityDescriptor now fails on a class cast exception, attempting to cast EntityDescriptor to EntitiesDescriptor