Boxplot only shows a <NULL> in x-axis

[akizminet]

Boxplot only shows a <NULL> on the example chart.

Generated query:

SELECT DATE_TRUNC('day', year) AS year,
       region AS region,
       sum("SP_POP_TOTL") AS "sum__SP_POP_TOTL"
FROM wb_health_population
WHERE year >= TO_TIMESTAMP('1960-01-01 00:00:00.000000', 'YYYY-MM-DD HH24:MI:SS.US')
  AND year < TO_TIMESTAMP('2021-10-04 04:03:20.000000', 'YYYY-MM-DD HH24:MI:SS.US')
GROUP BY DATE_TRUNC('day', year),
         region
LIMIT 50000;

How to reproduce the bug

1. Clone superset from github and start with docker-compose -f docker-compose-non-dev.yml up -d
2. Login and go to Chart. Choose Box plot
3. See error

Expected results

Boxplot shows multiple regions in x-axis

Actual results

Boxplot only shows a NULL in x-axis

Screenshots

Environment

• browser type and version: Chrome 94
• superset version: Superset 0.0.0dev
• python version: 3.7.9
• any feature flags active: None

Checklist

Make sure to follow these steps before submitting your issue - thank you!

• I have reproduced the issue with at least the latest released version of superset.
• I have checked the issue tracker for the same issue and I haven't found one similar.

[bayesfactor]

I have the same issue with boxplot on v0.0.0dev, Firefox