Query assigning a null to a column if a dependent column is also null in sql

Question

I have a table that contains dozens of athletes and the hours they spent at the gym everyday. My goal is to calculate their total hours in a month. They were supposed to go every day, and if they missed any day (null for that day), I want the entire total hours column for that athlete to display null, not the sum of their monthly hours. I have two columns, daily_hours, and total_hours, which is defined as sum(daily_hours). My query is this, however it is giving me an error in syntax

select case
  when daily_hours is null then total_hours = null 
  else total_hours end as name, total_hours 
from (select name, sum(daily_hours) as total_hours from athletes group by name);