MySQL query for time chart

I have a field called 'datepromised' that has data like:

2020/03/23 21:46
2020/06/20 22:00
2020/07/06 16:04
2020/07/06 19:55
2021/02/03 17:00
2021/02/03 17:31
2021/02/04 09:00
2021/02/04 11:30

What I am trying to achieve is to have a daily line chart of hours and above each hour would be a count of the requests.

Similar to:
https://www.researchgate.net/profile/Michal_Maciejewski2/publication/291556317/figure/fig1/AS:379866991087616@1467578756122/Hourly-request-submissions-and-active-taxicabs-The-average-taxi-serves-less-than-one.png


I would like the baseline of my chart to start at 00, 01, 02, 03, etc through 24 and show the count above each hour.

I have the MySQL doing the query correctly for extracting the data for the current date.

Question: How do I get the empty hours to still show.
I am looking for the data to look like:

theHour | numberOfItems
00 | 0
01 | 0
02 | 1
03 | 3
04 | 1
etc. through 24.

What I am currently getting is:

theHour | numberOfItems

17 | 2 (I ran this on FEB 3, so this I only had two requests at 17:00 for this day as shown in the data example above)


The MySQL query that I am using is:

SELECT
EXTRACT(hour from datepromised) AS theHour,
COUNT(*) AS numberOfItems
FROM makeready
WHERE (DATE(datepromised) = CURDATE())
GROUP BY EXTRACT(hour from datepromised)
ORDER BY EXTRACT(hour from datepromised)

Just can not figure out how to add the "empty hours" so the chart shows the full 24 hours on the baseline even if they are empty and if so, populate with at zero.

Any direction greatly appreciated.

Paul