Try the following:

Add a new column named "EmptyDate" then whenever you want set YourDateColumn = EmptyDate

Which action are you using? I was only able to get this to work when using Update Item, but not Update Multiple Items. I simply created a date variable in the workflow and then updated the item to that empty date variable.

I am using Update Item action only, I have tried your solution, but I am getting error and my workflow gets suspended for this particular action" Undefined variable" if my date variable value is empty.I am working on the Nintex workflow for office 365. Are you also working on the Nintex workflow for office 365?

I have already tried your solution, but it is not working for me. I am using Nintex workflow for office 365.

What kind of column is it? I have used Date/time field.

I too have this issue on Nintex 365. There is no working example of this on Nintex O365. What is Nintex doing to fix this?

1) Have tried the various suggestions on creating a Null Variable.
https://itgroove.net/mmman/2013/02/27/how-to-clear-a-date-field-in-a-nintex-workflow/ 

Nintex Workflow for Office 365 - Empty Date - Vadim Tabakman 

2) Have also tried copying a Blank Date from a dedicated "Workflow Variable" list holding in it just a blank Date Value. 
Can you clear a date column with a workflow in O365. All solutions seem to be for on premise 

3) Tried the Convert Value action suggested here, also does not work in 365. 
Empty date column with workflow 

None of these work! How hard can it be to simply reset a Date to BLANK VALUE.

Apparently, VERY Hard, as the easy things are ALWAYS HARD!

Hi Lance,

Finally I got the solution for this issue.

I have used action "Office 365 update items" and then added date/time value blank and publish the workflow. It will reset your date field value null. Please let me know if you have any question.

Thanks a bunch! I can confirm this solution works for both Date Fields with and without Time.

Hello Charul,

I used the "Office 365 update items" action  and my workflow gets suspended, can you please let me know the configuration steps to overcome this error.

Can you please share some screen shots of how you configured this action?

Thank you.

I can get it to work with the below config settings: 

Thanks Ben, it worked.

My part of the work was to update the Date field in the secondary list and it took some time to configure the filter list and finally its working. Thanks again.