Merge pull request #3536 from Naereen/patch-1

Prevent a TypeError bug for get_full_modname()

sphinx/util/__init__.py

@@ -282,6 +282,10 @@ def get_module_source(modname):
 
 def get_full_modname(modname, attribute):
     # type: (str, unicode) -> unicode
+    if modname is None:
+        # Prevents a TypeError: if the last getattr() call will return None
+        # then it's better to return it directly
+        return None
     __import__(modname)
     module = sys.modules[modname]