/Users/shaddeler/Developer/run/Homestead/scripts/homestead.rb:169:in `+': no implicit conversion of nil into String (TypeError)
from /Users/shaddeler/Developer/run/Homestead/scripts/homestead.rb:169:in `block (2 levels) in configure'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/plugins/kernel_v2/config/vm_provisioner.rb:72:in `call'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/plugins/kernel_v2/config/vm_provisioner.rb:72:in `add_config'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/plugins/kernel_v2/config/vm.rb:324:in `provision'
from /Users/shaddeler/Developer/run/Homestead/scripts/homestead.rb:168:in `block in configure'
from /Users/shaddeler/Developer/run/Homestead/scripts/homestead.rb:157:in `each'
from /Users/shaddeler/Developer/run/Homestead/scripts/homestead.rb:157:in `configure'
from /Users/shaddeler/Developer/run/Homestead/Vagrantfile:30:in `block in <top (required)>'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/config/v2/loader.rb:37:in `call'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/config/v2/loader.rb:37:in `load'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/config/loader.rb:113:in `block (2 levels) in load'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/config/loader.rb:107:in `each'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/config/loader.rb:107:in `block in load'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/config/loader.rb:104:in `each'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/config/loader.rb:104:in `load'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/vagrantfile.rb:28:in `initialize'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/environment.rb:746:in `new'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/environment.rb:746:in `vagrantfile'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/environment.rb:492:in `host'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/environment.rb:214:in `block in action_runner'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/action/runner.rb:33:in `call'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/action/runner.rb:33:in `run'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/environment.rb:479:in `hook'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/lib/vagrant/environment.rb:728:in `unload'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/bin/vagrant:177:in `ensure in <main>'
from /opt/vagrant/embedded/gems/gems/vagrant-1.8.6/bin/vagrant:177:in `<main>'
我在使用 vagrant up 命令时遇到了这个错误。