PivotTable vs PivotTableV2. String aggregation is incorrect in PivotTableV2

[tsarangi]

When the Aggregation Column is a String/Text, PivotTableV2 fails to show the values, where as PivotTable correctly shows it.
For example, in SQL syntax, one can do MAX(filed_that_is_a_string), and it would show you just the value, but in case of PivotTableV2 it shows Null, NaN, NaNUndefined, depending on the aggregation option, and none of them work.

Here is how to reproduce the bug:

I used the public.FCC 2018 Survey Dataset and the following columns:

• MAX(marital_status) as the aggregation, or metric
• In case of PivotTableV2, Row is is_self_employed and Column is bootcamp_attend
• In case of PivotTable, is_self_employed is in GROUP BY, bootcamp_attend is in Column and MAX(marital_status) is in metric.
• Follow the Screenshots attached to create a version of your own Chart and you will see PivotTable doesn't show the metric results, where it should.

Screenshots

Environment

(please complete the following information):

• browser type: Chrome
• superset version: HEAD of master branch: ac2545e
• python version: 3

Let me know what else you would like to see, I would try to provide.

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