diff --git a/docs/sphinxext/github.py b/docs/sphinxext/github.py
index a24b5a6..f56181e 100644
--- a/docs/sphinxext/github.py
+++ b/docs/sphinxext/github.py
@@ -51,7 +51,7 @@ def make_link_node(rawtext, app, type, slug, options):
                            **options)
     return node
 
-def ghissue_role(name, rawtext, text, lineno, inliner, options={}, content=[]):
+def ghissue_role(name, rawtext, text, lineno, inliner, options=None, content=None):
     """Link to a GitHub issue.
 
     Returns 2 part tuple containing list of nodes to insert into the
@@ -66,6 +66,8 @@ def ghissue_role(name, rawtext, text, lineno, inliner, options={}, content=[]):
     :param options: Directive options for customization.
     :param content: The directive content for customization.
     """
+    if options is None:
+        options = {}
 
     try:
         issue_num = int(text)
@@ -92,7 +94,7 @@ def ghissue_role(name, rawtext, text, lineno, inliner, options={}, content=[]):
     node = make_link_node(rawtext, app, category, str(issue_num), options)
     return [node], []
 
-def ghuser_role(name, rawtext, text, lineno, inliner, options={}, content=[]):
+def ghuser_role(name, rawtext, text, lineno, inliner, options=None, content=None):
     """Link to a GitHub user.
 
     Returns 2 part tuple containing list of nodes to insert into the
@@ -107,13 +109,16 @@ def ghuser_role(name, rawtext, text, lineno, inliner, options={}, content=[]):
     :param options: Directive options for customization.
     :param content: The directive content for customization.
     """
+    if options is None:
+        options = {}
+
     app = inliner.document.settings.env.app
     #info('user link %r' % text)
     ref = 'https://www.github.com/' + text
     node = nodes.reference(rawtext, text, refuri=ref, **options)
     return [node], []
 
-def ghcommit_role(name, rawtext, text, lineno, inliner, options={}, content=[]):
+def ghcommit_role(name, rawtext, text, lineno, inliner, options=None, content=None):
     """Link to a GitHub commit.
 
     Returns 2 part tuple containing list of nodes to insert into the
@@ -128,6 +133,9 @@ def ghcommit_role(name, rawtext, text, lineno, inliner, options={}, content=[]):
     :param options: Directive options for customization.
     :param content: The directive content for customization.
     """
+    if options is None:
+        options = {}
+
     app = inliner.document.settings.env.app
     #info('user link %r' % text)
     try: