CircularValidation doesnt work with an estimator using SelectTarget

[YanisLalou]

By using SelectTarget, the estimator only sees the target samples/labels/domains. However to compute the CircularValidation we need to train the estimator on the source THEN the target samples. Thus ValueError: Found array with 0 sample(s) (shape=(0, 2)) while a minimum of 1 is required. appears during the scoring of the method.

Solution: Return the default scorer instead ?