private static Optional<String> tryDownload(String url) {
		try {
			Catalog.getByRef(url);
			Util.verboseMsg("Catalog found at " + url);
			return Optional.of(url);
		} catch (Exception ex) {
			Util.verboseMsg("No catalog found at " + url, ex);
			return Optional.empty();
		}
	}
Return ImplicitCatalogRef if can be parsed into a git accessible structure.

@param name
@return null if cannot parse it
src/main/java/dev/jbang/catalog/ImplicitCatalogRef.java