I can't remove whitespaces from a string parsed by Nokogiri

strip only removes ASCII whitespace and the character you've got here is a Unicode non-breaking space.

Removing the character is easy. You can use gsub by providing a regex with the character code:

gsub(/\u00a0/, '')

You could also call

gsub(/[[:space:]]/, '')

to remove all Unicode whitespace. For details, check the Regexp documentation.