Allow data store to work even if file path is nil

lib/vagrant/data_store.rb

@@ -21,10 +21,11 @@ module Vagrant
 
     def initialize(file_path)
       @logger    = Log4r::Logger.new("vagrant::datastore")
+
+      if file_path
         @logger.info("Created: #{file_path}")
 
         @file_path = Pathname.new(file_path)
-
         if @file_path.exist?
           raise Errors::DotfileIsDirectory if @file_path.directory?
 
@@ -35,11 +36,19 @@ module Vagrant
             @logger.error("Data store contained invalid JSON. Ignoring.")
           end
         end
+      else
+        @logger.info("No file path. In-memory data store.")
+        @file_path = nil
+      end
     end
 
     # Commits any changes to the data to disk. Even if the data
     # hasn't changed, it will be reserialized and written to disk.
     def commit
+      if !@file_path
+        raise StandardError, "In-memory data stores can't be committed."
+      end
+
       clean_nil_and_empties
 
       if empty?

test/unit/vagrant/data_store_test.rb

@@ -64,4 +64,16 @@ describe Vagrant::DataStore do
     # The file should no longer exist
     db_file.should_not be_exist
   end
+
+  it "works if the DB file is nil" do
+    store = described_class.new(nil)
+    store[:foo] = "bar"
+    store[:foo].should == "bar"
+  end
+
+  it "throws an exception if attempting to commit a data store with no file" do
+    store = described_class.new(nil)
+    expect { store.commit }.
+      to raise_error(StandardError)
+  end
 end