In older versions adoDB lite had:
..._Resulset::Fields($field = -1)
or similar, and if no value was specified all the fields were returned.
Now instead there is no implicit value for $field and $field is checked through empty. This is not suggested, as if the field starts with a zero '0' (might be possible in some dbmses using quotes) empty will be evaluated to true.
I suggest the usage of the implicit value $field = null and a check with isset() which would be 100% safe.