from_columns errors when a column is blank about xport

[selik]

If the column is blank, you'd rather have it implicitly fill with NaN or None? How would we determine if it's a numeric or text column? My initial thought was that raising an error is more explicit. Perhaps the error message could be better, explaining why an implicit action is difficult to decide on.

[selik]

Currently no column can be blank:

if not all(mapping.values()):
    raise ValueError('all columns must have at least one element')

This seems like a fairly clear error message. At least one value is necessary for every column to infer whether the column should be numeric or text.