in src/main/java/org/apache/sling/resourcemerger/impl/MergingResourceProvider.java [190:196]
public Resource getParent(ResolveContext<Void> ctx, Resource child) {
final String parentPath = ResourceUtil.getParent(child.getPath());
if (parentPath == null) {
return null;
}
return this.getResource(ctx, parentPath, ResourceContext.EMPTY_CONTEXT, child);
}