From 9a37828bd2d009fbe34aeb4128be6a606640775c Mon Sep 17 00:00:00 2001
From: Geoffrey Sneddon <geoffers@gmail.com>
Date: Sat, 17 May 2014 21:48:32 +0100
Subject: [PATCH] Fix optionaltags filter to not error when filtering nothing.

---
 html5lib/filters/optionaltags.py           | 3 ++-
 html5lib/tests/test_optionaltags_filter.py | 7 +++++++
 2 files changed, 9 insertions(+), 1 deletion(-)
 create mode 100644 html5lib/tests/test_optionaltags_filter.py

diff --git a/html5lib/filters/optionaltags.py b/html5lib/filters/optionaltags.py
index fefe0b30..88e5ff47 100644
--- a/html5lib/filters/optionaltags.py
+++ b/html5lib/filters/optionaltags.py
@@ -11,7 +11,8 @@ def slider(self):
                 yield previous2, previous1, token
             previous2 = previous1
             previous1 = token
-        yield previous2, previous1, None
+        if previous1 is not None:
+            yield previous2, previous1, None
 
     def __iter__(self):
         for previous, token, next in self.slider():
diff --git a/html5lib/tests/test_optionaltags_filter.py b/html5lib/tests/test_optionaltags_filter.py
new file mode 100644
index 00000000..cd282149
--- /dev/null
+++ b/html5lib/tests/test_optionaltags_filter.py
@@ -0,0 +1,7 @@
+from __future__ import absolute_import, division, unicode_literals
+
+from html5lib.filters.optionaltags import Filter
+
+
+def test_empty():
+    assert list(Filter([])) == []