Empty attributes render as real, empty attributes. Patch thanks to Jan Szumiec!

git-svn-id: svn://hamptoncatlin.com/haml/trunk@574 7063305b-7217-0410-af8c-cdc13e5119b9

lib/haml/engine.rb

@@ -684,8 +684,8 @@ END
       @other_quote_char = @options[:attr_wrapper] == '"' ? "'" : '"'
   
       result = attributes.collect do |a,v|
+        unless v.nil? 
           v = v.to_s
-        unless v.nil? || v.empty?
           attr_wrapper = @options[:attr_wrapper]
           if v.include? attr_wrapper
             if v.include? @other_quote_char

test/haml/results/just_stuff.xhtml

@@ -29,7 +29,8 @@ stuff followed by whitespace
   <strong>there can even be sub-tags!</strong>
   Or script!
 -->
-<p>class attribute shouldn't appear!</p>
+<p class=''>class attribute should appear!</p>
+<p>this attribute shouldn't appear</p>
 <!--[if lte IE6]> conditional comment! <![endif]-->
 <!--[if gte IE7]> 
   <p>Block conditional comment</p>

test/haml/templates/just_stuff.haml

@@ -33,7 +33,8 @@
 -#
   Nested Haml comment
   - raise 'dead'
-%p{ :class => "" } class attribute shouldn't appear!
+%p{ :class => "" } class attribute should appear!
+%p{ :gorbachev => nil } this attribute shouldn't appear
 /[if lte IE6] conditional comment!
 /[if gte IE7]
   %p Block conditional comment