As you can see in the final sentence "...modifying the setting in null". In null doesn't appear to be very explicit. This is in build 18.104.22.168
Ummm, forum doesn't appear to let me add images. The full text on the popup window is
"Memory is running low
747 used of 773 maximum MB
Memory can be reduced by closing applications and projects not in use
Memory can be increased by modifying the setting in null"