Allow filters without nested text.

lib/haml/precompiler.rb

@@ -668,7 +668,6 @@ END
     # Starts a filtered block.
     def start_filtered(name)
       raise HamlError.new("Invalid filter name \":#{name}\"") unless name =~ /^\w+$/
-      raise SyntaxError.new('Filters must have nested text.') unless @block_opened
 
       unless filter = options[:filters][name]
         if filter == 'redcloth' || filter == 'markdown' || filter == 'textile'

test/haml/engine_test.rb

@@ -5,7 +5,6 @@ class EngineTest < Test::Unit::TestCase
   EXCEPTION_MAP = {
     "!!!\n  a" => "Illegal Nesting: Nesting within a header command is illegal.",
     "a\n  b" => "Illegal Nesting: Nesting within plain text is illegal.",
-    ":a" => "Filters must have nested text.",
     "/ a\n  b" => "Illegal Nesting: Nesting within a tag that already has content is illegal.",
     "% a" => 'Invalid tag: "% a"',
     "%p a\n  b" => "Illegal Nesting: Content can't be both given on the same line as %p and nested within it.",
@@ -439,6 +438,16 @@ class EngineTest < Test::Unit::TestCase
     end    
   end
 
+  def test_empty_filter
+    assert_equal(<<END, render(':javascript'))
+<script type='text/javascript'>
+  //<![CDATA[
+    
+  //]]>
+</script>
+END
+  end
+
   def test_local_assigns_dont_modify_class
     assert_equal("bar\n", render("= foo", :locals => {:foo => 'bar'}))
     assert_equal(nil, defined?(foo))