Fix bug with empty select list

lib/webrat/field.rb

@@ -237,6 +237,7 @@ module Webrat
       selected_options = @element / "option[@selected='selected']"
       selected_options = @element / "option:first" if selected_options.empty? 
       selected_options.map do |option|
+        return "" if option.nil?
         option["value"] || option.innerHTML
       end
     end

test/selects_test.rb

@@ -57,6 +57,17 @@ class SelectsTest < Test::Unit::TestCase
     @session.clicks_button
   end
 
+  def test_should_work_with_empty_select_lists
+    @response.stubs(:body).returns(<<-EOS)
+      <form method="post" action="/login">
+        <select name="month"></select>
+        <input type="submit" />
+      </form>
+    EOS
+    @session.expects(:post_via_redirect).with("/login", 'month' => '')
+    @session.clicks_button
+  end
+  
   def test_should_work_without_specifying_the_field_name_or_label
     @response.stubs(:body).returns(<<-EOS)
       <form method="post" action="/login">