docs: protected void registerNamespace(
  		SqlValidatorScope usingScope,
  		String alias,
  		SqlValidatorNamespace ns,
  		boolean forceNullable) {
  		namespaces.put(ns.getNode(), ns);
  		if (usingScope != null) {
  			usingScope.addChild(ns, alias, forceNullable);
  		}
  	}