[feaLib] Correctly handle <NULL> in single pos lookups #3803
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anthrotype
approved these changes
Apr 23, 2025
bool(ValueRecord()) evaluates to False, which means "pos foo <NULL>;" gets serialized to "pos foo ;" which is invalid.
This was causing an AssertionError:
File "/fonttools/Lib/fontTools/otlLib/builder.py", line 1528, in can_add
assert isinstance(value, ValueRecord)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError
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<NULL>in single pos statements was broken (it was skipped resulting in invalid feature code).AFDKO’s makeotf does not support
<NULL>at all, but we support it in pair pos lookups, so this is not much different. It might not be of much value, but it is something OpenType layout supports and it is causing round tripping issue for some code I’m working on.