I am having trouble with line breaks being inserted into group_concat string when the value is non-existent (null).

So here's the (joined) table, for example:

Letter | Number

A | 1

B | 2

C | null

D | 4

E | null

F | 2

so if I do:

group_concat(DISTINCT "Number" SEPARATOR ', ')

I would expect result being: '1, 2, 4'

However, whatever I tried, I am getting:

1, 2

, 4

Can anyone help?