Use "is None" instead of "== None"
The latter hits the __eq__ method and can fail because we now
do not allow comparing objects of different types.
For example, was failing subsetting Andika-R.ttf.
diff --git a/Lib/fontTools/ttLib/tables/otBase.py b/Lib/fontTools/ttLib/tables/otBase.py
index bf010b5..37d109d 100644
--- a/Lib/fontTools/ttLib/tables/otBase.py
+++ b/Lib/fontTools/ttLib/tables/otBase.py
@@ -373,7 +373,7 @@
continue
if appendExtensions:
- assert extTables != None, "Program or XML editing error. Extension subtables cannot contain extensions subtables"
+ assert extTables is not None, "Program or XML editing error. Extension subtables cannot contain extensions subtables"
newDone = {}
item._gatherTables(extTables, None, newDone)