Fix index generation issue

Index keys were wrongly defined as empty string which caused garbage in
the resulting index this commit changes the empty string to None. The
version number has been incremented.

CHANGES.rst

@@ -1,6 +1,11 @@
 Changes
 =======
 
+0.2.4 - unreleased
+------------------
+
+* fix index generation issue
+
 0.2.3 - 2016-05-05
 ------------------
 

jandd/sphinxext/ip.py

@@ -23,7 +23,7 @@ from sphinx.locale import l_
 from sphinx.roles import XRefRole
 from sphinx.util.nodes import make_refnode
 
-__version__ = '0.2.3'
+__version__ = '0.2.4'
 
 
 def ip_object_anchor(typ, path):
@@ -120,8 +120,8 @@ class IPRange(Directive):
             doctitle = self.state.document.traverse(nodes.title)[0].astext()
         idx_text = "%s; %s" % (self.rangespec, doctitle)
         self.indexnode = addnodes.index(entries=[
-            ('single', idx_text, name, '', ''),
-            ('single', self.get_index_text(), name, '', '')
+            ('single', idx_text, name, '', None),
+            ('single', self.get_index_text(), name, '', None)
         ])
 
         if self.content:

setup.py

@@ -2,7 +2,7 @@
 
 from setuptools import setup, find_packages
 
-version = '0.2.3'
+version = '0.2.4'
 
 with open('README.rst') as readme:
     description = readme.read() + "\n\n"