Details of a Rubinius-specific error when using the pdf-reader gem

stack_trace_from_an_app.txt

TypeError: String#append primitive only accepts Strings
        from kernel/bootstrap/string.rb:25:in `append'
        from kernel/common/string19.rb:623:in `<<'
        from /home/jw/.rvm/gems/rbx-head/gems/pdf-reader-1.3.3/lib/pdf/reader/buffer.rb:307:in `prepare_regular_token'
                   ( https://github.com/yob/pdf-reader/blob/v1.3.3/lib/pdf/reader/buffer.rb#L307 )
        from /home/jw/.rvm/gems/rbx-head/gems/pdf-reader-1.3.3/lib/pdf/reader/buffer.rb:174:in `prepare_tokens'
                   ( https://github.com/yob/pdf-reader/blob/v1.3.3/lib/pdf/reader/buffer.rb#L174 )
        from kernel/common/integer.rb:83:in `times'
        from /home/jw/.rvm/gems/rbx-head/gems/pdf-reader-1.3.3/lib/pdf/reader/buffer.rb:170:in `prepare_tokens'
        from /home/jw/.rvm/gems/rbx-head/gems/pdf-reader-1.3.3/lib/pdf/reader/buffer.rb:116:in `token'
        from /home/jw/.rvm/gems/rbx-head/gems/pdf-reader-1.3.3/lib/pdf/reader/parser.rb:73:in `parse_token'
        from /home/jw/.rvm/gems/rbx-head/gems/pdf-reader-1.3.3/lib/pdf/reader/page.rb:138:in `content_stream'
        from /home/jw/.rvm/gems/rbx-head/gems/pdf-reader-1.3.3/lib/pdf/reader/page.rb:105:in `walk'
        from /home/jw/.rvm/gems/rbx-head/gems/pdf-reader-1.3.3/lib/pdf/reader/page.rb:75:in `text'
        from /projects/physioage/cmv_trial/lib/sabater_lab_report.rb:32:in `patient_data_line'
        from /projects/physioage/cmv_trial/lib/sabater_lab_report.rb:37:in `patient_data'
        from /projects/physioage/cmv_trial/lib/sabater_lab_report.rb:80:in `to_report'
        from (irb):20
        from kernel/common/block_environment.rb:55:in `call_on_instance'
        from kernel/common/eval.rb:73:in `eval'
        from kernel/common/kernel19.rb:42:in `loop'
        from kernel/bootstrap/proc.rb:22:in `call'
        from kernel/common/throw_catch19.rb:8:in `catch'
        from kernel/common/throw_catch.rb:10:in `register'
        from kernel/common/throw_catch19.rb:7:in `catch'
        from kernel/bootstrap/proc.rb:22:in `call'
        from kernel/common/throw_catch19.rb:8:in `catch'
        from kernel/common/throw_catch.rb:10:in `register'
        from kernel/common/throw_catch19.rb:7:in `catch'
        from kernel/delta/codeloader.rb:68:in `load_script'
        from kernel/delta/codeloader.rb:119:in `load_script'
        from kernel/loader.rb:652:in `script'
        from kernel/loader.rb:853:in `main'rubinius-2.0.0.rc1 :021

stack_trace_from_reproducable_repo.txt

jw@logopolis:/projects/open/rubinius_vs_pdf_reader$ ruby issue.rb
An exception occurred running issue.rb
    String#append primitive only accepts Strings (TypeError)

Backtrace:
                  String#append at kernel/bootstrap/string.rb:25
                      String#<< at kernel/common/string19.rb:623
  PDF::Reader::Buffer#prepare_regular_token at \
          /home/jw/.rvm/gems/rbx-head/gems/pdf-reader-1.3.3/lib/pdf/reader/buffer.rb:307
  { } in PDF::Reader::Buffer#prepare_tokens at \
          /home/jw/.rvm/gems/rbx-head/gems/pdf-reader-1.3.3/lib/pdf/reader/buffer.rb:174
          Integer(Fixnum)#times at kernel/common/integer.rb:83
 PDF::Reader::Buffer#prepare_tokens at /home/jw/.rvm/gems
                                       /rbx-head/gems
                                       /pdf-reader-1.3.3/lib/pdf
                                       /reader/buffer.rb:170
     PDF::Reader::Buffer#token at /home/jw/.rvm/gems/rbx-head
                                  /gems/pdf-reader-1.3.3/lib/pdf
                                  /reader/buffer.rb:116
 PDF::Reader::Parser#parse_token at /home/jw/.rvm/gems/rbx-head
                                    /gems/pdf-reader-1.3.3/lib
                                    /pdf/reader/parser.rb:73
 PDF::Reader::Page#content_stream at /home/jw/.rvm/gems/rbx-head
                                     /gems/pdf-reader-1.3.3/lib
                                     /pdf/reader/page.rb:138
        PDF::Reader::Page#walk at /home/jw/.rvm/gems/rbx-head
                                  /gems/pdf-reader-1.3.3/lib/pdf
                                  /reader/page.rb:105
        PDF::Reader::Page#text at /home/jw/.rvm/gems/rbx-head
                                  /gems/pdf-reader-1.3.3/lib/pdf
                                  /reader/page.rb:75
              Object#__script__ at issue.rb:7
 Rubinius::CodeLoader#load_script at kernel/delta
                                     /codeloader.rb:68
 Rubinius::CodeLoader.load_script at kernel/delta
                                     /codeloader.rb:119
        Rubinius::Loader#script at kernel/loader.rb:652
          Rubinius::Loader#main at kernel/loader.rb:853

see https://github.com/mustmodify/rubinius_vs_pdf_reader