Footnotes filter raises 500 error for erroneous content
Sentry error: https://new-sentry.gitlab.net/organizations/gitlab/issues/725401
NoMethodError: undefined method `delete_prefix' for nil:NilClass
ref_num = link_node[:id].delete_prefix(FOOTNOTE_LINK_ID_PREFIX)
^^^^^^^^^^^^^^
from lib/banzai/filter/footnote_filter.rb:40:in `block in call'
from nokogiri-1.16.0-x86_64 (linux) lib/nokogiri/xml/node_set.rb:235:in `block in each'
from nokogiri-1.16.0-x86_64 (linux) lib/nokogiri/xml/node_set.rb:234:in `upto'
from nokogiri-1.16.0-x86_64 (linux) lib/nokogiri/xml/node_set.rb:234:in `each'
from lib/banzai/filter/footnote_filter.rb:39:in `call'
from html-pipeline (2.14.3) lib/html/pipeline/filter.rb:129:in `call'
from html-pipeline (2.14.3) lib/html/pipeline.rb:134:in `block in perform_filter'
from html-pipeline (2.14.3) lib/html/pipeline.rb:172:in `instrument'
from html-pipeline (2.14.3) lib/html/pipeline.rb:133:in `perform_filter'
from html-pipeline (2.14.3) lib/html/pipeline.rb:119:in `block (2 levels) in call'
from html-pipeline (2.14.3) lib/html/pipeline.rb:118:in `each'
from html-pipeline (2.14.3) lib/html/pipeline.rb:118:in `inject'
from html-pipeline (2.14.3) lib/html/pipeline.rb:118:in `block in call'
from html-pipeline (2.14.3) lib/html/pipeline.rb:172:in `instrument'