NoMethodError: undefined method `[]' for nil:NilClass

https://sentry.gitlab.net/gitlab/gitlabcom/issues/2430778/?referrer=gitlab_plugin

NoMethodError: undefined method `[]' for nil:NilClass
  gitlab/ci/parsers/coverage/cobertura.rb:39:in `parse_node'
    if key == 'sources' && value['source'].present?
  gitlab/ci/parsers/coverage/cobertura.rb:34:in `block in parse_all'
    parse_node(key, value, coverage_report, context)
  gitlab/ci/parsers/coverage/cobertura.rb:33:in `each'
    root.each do |key, value|
  gitlab/ci/parsers/coverage/cobertura.rb:33:in `parse_all'
    root.each do |key, value|
  gitlab/ci/parsers/coverage/cobertura.rb:53:in `parse_node'
    parse_all(value, coverage_report, context)
...
(114 additional frame(s) were not displayed)

undefined method `[]' for nil:NilClass