Provide generator parameter only when actual resolution is expected to happen (idea: PostponedReference doesn't depend on TemplateGenerator, its resolution does). PostponedReference is not expected to be queried for target model/node unless resolved (for now resolved == replaced, so might be UnsupportedOpEx. There're plans, however =, to split resolution from replacement later).
Refactor: remove duplicating code
Allow any link to answer whether it's multiple or not. The fact ReferenceLinks can not be multiple in the MPS's metamodel (at least now) is hidden in the SReferenceLinkAdapter implementation.
Use actual replacement child