Don't forward ports if there aren't any to forward

CHANGELOG.md

@@ -4,6 +4,7 @@
   - `vagrant ssh` does a direct `exec()` syscall now instead of going through
     the shell. This makes it so things like shell expansion oddities no longer
     cause problems. [GH-715]
+  - Fix crashing case if there are no ports to forward.
 
 ## 0.9.5 (February 5, 2012)
 

lib/vagrant/action/vm/forward_ports.rb

@@ -81,7 +81,10 @@ module Vagrant
             ports << options.merge(:name => options[:name], :adapter => options[:adapter])
           end
 
-          @env[:vm].driver.forward_ports(ports)
+          if !ports.empty?
+            # We only need to forward ports if there are any to forward
+            @env[:vm].driver.forward_ports(ports)
+          end
         end
       end
     end

lib/vagrant/driver/virtualbox_4_0.rb

@@ -144,7 +144,7 @@ module Vagrant
                        pf_builder.join(",")])
         end
 
-        execute("modifyvm", @uuid, *args)
+        execute("modifyvm", @uuid, *args) if !args.empty?
       end
 
       def halt

lib/vagrant/driver/virtualbox_4_1.rb

@@ -144,7 +144,7 @@ module Vagrant
                        pf_builder.join(",")])
         end
 
-        execute("modifyvm", @uuid, *args)
+        execute("modifyvm", @uuid, *args) if !args.empty?
       end
 
       def halt