notitle document attribute throws exception

[veeg]

I'm attempting to render a document without a title page using the :notitle: document attribute

:notitle:
= Test

Results in the following trace

user@host:~> asciidoctor-pdf.ruby2.1 test.adoc --trace
/usr/lib64/ruby/gems/2.1.0/gems/prawn-2.0.2/lib/prawn/document.rb:668:in `generate_margin_box': undefined method `margins' for nil:NilClass (NoMethodError)
    from /usr/lib64/ruby/gems/2.1.0/gems/prawn-2.0.2/lib/prawn/document.rb:307:in `go_to_page'
    from /usr/lib64/ruby/gems/2.1.0/gems/asciidoctor-pdf-1.5.0.alpha.10/lib/asciidoctor-pdf/prawn_ext/extensions.rb:600:in `delete_page'
    from /usr/lib64/ruby/gems/2.1.0/gems/asciidoctor-pdf-1.5.0.alpha.10/lib/asciidoctor-pdf/converter.rb:168:in `convert_document'
    from /usr/lib64/ruby/gems/2.1.0/gems/asciidoctor-pdf-1.5.0.alpha.10/lib/asciidoctor-pdf/converter.rb:98:in `convert'
    from /usr/lib64/ruby/gems/2.1.0/gems/asciidoctor-1.5.3/lib/asciidoctor/document.rb:1044:in `convert'
    from /usr/lib64/ruby/gems/2.1.0/gems/asciidoctor-1.5.3/lib/asciidoctor.rb:1514:in `convert'
    from /usr/lib64/ruby/gems/2.1.0/gems/asciidoctor-1.5.3/lib/asciidoctor/cli/invoker.rb:94:in `block in invoke!'
    from /usr/lib64/ruby/gems/2.1.0/gems/asciidoctor-1.5.3/lib/asciidoctor/cli/invoker.rb:86:in `each'
    from /usr/lib64/ruby/gems/2.1.0/gems/asciidoctor-1.5.3/lib/asciidoctor/cli/invoker.rb:86:in `invoke!'
    from /usr/lib64/ruby/gems/2.1.0/gems/asciidoctor-pdf-1.5.0.alpha.10/bin/asciidoctor-pdf:27:in `<top (required)>'
    from /usr/bin/asciidoctor-pdf.ruby2.1:23:in `load'
    from /usr/bin/asciidoctor-pdf.ruby2.1:23:in `<main>'

Using the following version/environment

Asciidoctor PDF 1.5.0.alpha.10 using Asciidoctor 1.5.3 [http://asciidoctor.org]
Runtime Environment (ruby 2.1.2p95 (2014-05-08 revision 45877) [x86_64-linux-gnu]) (lc:UTF-8 fs:UTF-8 in:- ex:UTF-8)

[mojavelinux]

It's a known issue that Asciidoctor PDF fails if your document has no content (aside from the document title). Add any amount of content and it will work. This is the same as #317.