Planner#parse can't parse DAY() function

import org.apache.calcite.sql.parser.SqlParseException;
import org.apache.calcite.sql.validate.SqlValidator;
import org.apache.calcite.tools.FrameworkConfig;
import org.apache.calcite.tools.Frameworks;
import org.apache.calcite.tools.Planner;

public class Main {
    public static void main(String[] args) throws SqlParseException {
        FrameworkConfig config = Frameworks.newConfigBuilder().build();
        {
            Planner planner = Frameworks.getPlanner(config);
            System.out.println(planner.parse("select months(t) from tbl"));
        }
        {
            Planner planner = Frameworks.getPlanner(config);
            System.out.println(planner.parse("select month(t) from tbl"));
        }
        {
            Planner planner = Frameworks.getPlanner(config);
            System.out.println(planner.parse("select hours(t) from tbl"));
        }
        {
            Planner planner = Frameworks.getPlanner(config);
            System.out.println(planner.parse("select hour(t) from tbl"));
        }
        {
            Planner planner = Frameworks.getPlanner(config);
            System.out.println(planner.parse("select days(t) from tbl"));
        }
        {
            Planner planner = Frameworks.getPlanner(config);
            // This throws `org.apache.calcite.sql.parser.SqlParseException: Encountered "day" ...`
            System.out.println(planner.parse("select day(t) from tbl"));
        }
    }
}