Your dependency file specified a branch or reference for asciidoctor-pdf, but Dependabot couldn't find it at the project's source. Has it been removed?
For Ruby dependencies, this can be caused by a branch specified in your Gemfile being deleted at the source, or having been rebased, so the commit reference in your Gemfile.lock is no longer included in the branch. In that case, it can be fixed by running bundler update asciidoctor-pdf locally.
Your dependency file specified a branch or reference for asciidoctor-pdf, but Dependabot couldn't find it at the project's source. Has it been removed?
For Ruby dependencies, this can be caused by a branch specified in your Gemfile being deleted at the source, or having been rebased, so the commit reference in your Gemfile.lock is no longer included in the branch. In that case, it can be fixed by running bundler update asciidoctor-pdf locally.