Several calls to generate_xy_splits in a notebook with no drop_columns specified causes KeyError

[david-ryan-alviola]

If generate_xy_splits is called without a list passed into drop_columns, a default list is constructed and the target is appended to it. However, calling generate_xy_splits again with no list passed in will attempt to append the new target to the default list resulting in a list of ['target1', 'target2']. The 'target1' key may not be in the new dataframe, resulting in a KeyError.

Recommend creating a new list each time generate_xy_splits is called.