Fix support for a file input which is not filled in.

lib/capybara/driver/rack_test_driver.rb

@@ -83,10 +83,12 @@ class Capybara::Driver::RackTest
         agg
       end
       params += node.xpath(".//input[@type='file']").inject([]) do |agg, input|
-        if multipart?
-          agg << [input['name'].to_s, Rack::Test::UploadedFile.new(input['value'].to_s)]
-        else
-          agg << [input['name'].to_s, File.basename(input['value'].to_s)]
+        if input['value'].to_s.any?
+          if multipart?
+            agg << [input['name'].to_s, Rack::Test::UploadedFile.new(input['value'].to_s)]
+          else
+            agg << [input['name'].to_s, File.basename(input['value'].to_s)]
+          end
         end
         agg
       end

spec/session_spec.rb

@@ -486,6 +486,10 @@ shared_examples_for "session" do
         @session.click_button('Upload')
         @session.body.should include(File.read(@test_file_path))
       end
+
+      it "should not break if no file is submitted" do
+        @session.click_button('Upload')
+      end
     end
 
   end

spec/test_app.rb

@@ -50,7 +50,7 @@ class TestApp < Sinatra::Base
   end
 
   post '/upload' do
-    params[:form][:document][:tempfile].read
+    params[:form][:document][:tempfile].read rescue ''
   end
 end
 

spec/views/form.erb

@@ -101,6 +101,11 @@
 </form>
 
 <form action="/upload" method="post" enctype="multipart/form-data">
+  <p>
+    <label for="form_name">Name</label>
+    <input type="file" name="form[name]" id="form_name"/>
+  </p>
+
   <p>
     <label for="form_document">Document</label>
     <input type="file" name="form[document]" id="form_document"/>