Updating a Point with CSVStorage throws a TypeError

[citrusvanilla]

Describe the bug
Updating a Point after insertion using CSVStorage throws a TypeError.

To Reproduce

from tinyflux import Point, TinyFlux
db = TinyFlux("my_db.tinyflux")
p = Point(fields={"a": 1})
db.insert(p)
db.update_all(fields=lambda x: {"b": 2})

Expected behavior
A TypeError should not be thrown.