How to delete multiple empty lines with SED?

Question

I'm trying to compress a text document by deleting of duplicated empty lines, with sed. This is what I'm doing (to no avail):

sed -i -E 's/\n{3,}/\n/g' file.txt

I understand that it's not correct, according to this manual, but I can't figure out how to do it correctly. Thanks.

Answer 1

As tripleee suggested above, I'm using Perl instead of sed:

perl -0777pi -e 's/\n{3,}/\n\n/g'