Whenever using next in a map loop you likely need to remove the nils

This is part of the Semicolon&Sons Code Diary - consisting of lessons learned on the job. You're in the algorithms category.

Last Updated: 2021-05-15

I deployed the following "fix" to another bug, only to discover it also failed:

def tag_list=(names)
  self.tags = names.split(',').map do |n|
    next if n.blank?

    Tag.where(name: n.strip).first_or_create!
  end
end

With input "instruments, ", the second entry was nil. So effectively this code boiled down to self.tags = [Tag<name: instrument>, nil]

But self.tags expects only tag entries. The nil cannot be handled. Kablam

Lesson

When calling bare next in a mapping loop, you need to anticipate nils in the output.