kwargs default value is not set after transformation

[yakobu]

from codetransformer import CodeTransformer, pattern
from codetransformer.instructions import BINARY_ADD, BINARY_MULTIPLY


class add2mul(CodeTransformer):
    @pattern(BINARY_ADD)
    def _add2mul(self, add_instr):
        yield BINARY_MULTIPLY().steal(add_instr)


def f(*, k=3):
    return k + 1


ff = add2mul()(f)

print(f.__kwdefaults__) => {'k': 3}
print(f()) => 4
print(ff.__kwdefaults__) => None
print(ff()) => TypeError: f() missing 1 required positional argument: 'k'