[R] dataimport: refine error detection Consider only None as non-expected value after parsing the input file. False is now allowed because of the boolean yesno checker that returns False by default.

"""pre 3.6 bw compat"""
# pylint: disable-msg=W0614,W0401
from warnings import warn
warn('moved to cubicweb.mixins', DeprecationWarning, stacklevel=2)
from cubicweb.mixins import *