これ出るようになっちゃったんですけど、原因わかりますかね

# portupgrade -a
/usr/local/lib/ruby/site_ruby/1.8/pkgdb.rb:323:in `deorigin': cannot convert nil into String (PkgDB::DBError)
from /usr/local/lib/ruby/site_ruby/1.8/pkgdb.rb:916:in `tsort_build'
from /usr/local/lib/ruby/site_ruby/1.8/pkgdb.rb:915:in `each'
from /usr/local/lib/ruby/site_ruby/1.8/pkgdb.rb:915:in `tsort_build'
from /usr/local/lib/ruby/site_ruby/1.8/pkgdb.rb:907:in `each'
from /usr/local/lib/ruby/site_ruby/1.8/pkgdb.rb:907:in `tsort_build'
from /usr/local/lib/ruby/site_ruby/1.8/pkgdb.rb:929:in `sort_build'
from /usr/local/lib/ruby/site_ruby/1.8/pkgdb.rb:933:in `sort_build!'
from /usr/local/sbin/portupgrade:674:in `main'
from /usr/local/sbin/portupgrade:207:in `initialize'
from /usr/local/sbin/portupgrade:207:in `new'
from /usr/local/sbin/portupgrade:207:in `main'
from /usr/local/sbin/portupgrade:1845