in datahub/models/types.py [0:0]
def validate_value(value, field):
if field.allow_null and field.type != FieldType.STRING and (value == '' or value == b''):
return None
datahub_type = _datahub_types_dict[field.type]
result = _validate_builtin_value(value, datahub_type)
datahub_type.validate_value(result)
return result