value

The step's result, whole and as its terminal produced it - the one thing a handle reaches.

After fetchFieldStrict<Int> this is the Int, after fetchObjectStrict<Senator> the Senator, after fetchRows the List<Row>. Taking a column, an element or a property out of one is map over that type.

Whether the step that uses the value can bind it is a separate question, answered by what the driver can send. A scalar goes, and a list of scalars goes as an array; a Row, a List<Row>, a Map or a class the type registry has never heard of does not, and is refused where the parameter is encoded, naming the class. map takes the part that can be sent, and spread turns a map into parameters of its own.