ActionView::Template::Error: no implicit conversion of String into Integer

https://sentry.gitlab.net/gitlab/gitlabcom/issues/4108196/?referrer=gitlab_plugin

TypeError: no implicit conversion of String into Integer
  app/models/blob_viewer/package_json.rb:14:in `yarn?'
    json_data['engines'].present? && json_data['engines']['yarn'].present?
  app/models/blob_viewer/package_json.rb:10:in `manager_name'
    yarn? ? 'yarn' : 'npm'
  app/views/projects/blob/viewers/_dependency_manager.html.haml:3:
    = _("This project manages its dependencies using %{strong_start}%{manager_name}%{strong_end}").html_safe % { manager_name: viewer.manager_name, strong_start: '<strong>'.html_safe, strong_end: '</strong>'.html_safe }
  app/views/projects/blob/viewers/_dependency_manager.html.haml:2:
    = succeed '.' do
  app/views/projects/blob/_viewer.html.haml:24:
    = render viewer.partial_path, viewer: viewer
...
(206 additional frame(s) were not displayed)

ActionView::Template::Error: no implicit conversion of String into Integer