Show null value on dimension only if value in another column isn't a duplicate

[lailarhc]

Hello.
I have two columns in a table which is the result of a union. I united two different tables which both contained information about courses that employees have taken. The result is that I now have rows with thhere both columns have non null values and rows where the column equivalent to courses have null values.

Here's what I want to do:
- I need to display in a KPI how many employees have not taken any courses, meaning I need to somehow only count the null values if the employee's name isn't a duplicated value.
- I need to display in a KPI how many employees have taken courses, which means I need to only count non null values (I think I have this one figured out)

- I need to display in a table employees that have taken courses and employees who have not, which means I need to ignore null values if the employee has already taken a course.

Here's a image to illustrate my problem.
Notice that the same employee seems to have both taken many courses and no course at all. If the employee has already taken a course then I need that row with the null value gone.

How can I go on about this?
I'll link a related post that I've written before:
Check if value exists in one table before selecting null value in another table 

Any suggestion is most welcome.
Thank you in advance.