Steps to reproduce the issue

Install Joomla 4.0 Nightly (22/03/2019)
Solve the stats.php bug #24303

1. Open a Module, click on Save, or Save&Close or Close.
2. Open an article, delete date & time from publishing fields, then click on Save or Save&Close.

Expected result

1. Module closed or saved or saved&closed without error.
2. Article saved or saved&closed without error

Actual result

1. After Close "An error has occurred. 1048 Column 'checked_out_time' cannot be null" OR
   After Save "Save failed with the following error: Column 'publish_up' cannot be null"
2. After Save "Error: Save failed with the following error: Incorrect datetime value: '' for column 'created' at row 1"

System information (as much as possible)

dbserver: mysql
dbversion: 5.5.5-10.1.38-MariaDB
dbcollation: utf8_general_ci
dbconnectioncollation: utf8_general_ci
phpversion: 7.2.14
server: Apache
sapi_name: litespeed
version: Joomla! 4.0.0-alpha8-dev Development [ Amani ] 9-March-2019 13:41 GMT
useragent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/73.0.3683.75 Safari/537.36

Additional comments

Some warnings in console:

DevTools failed to parse SourceMap: https://mywebsite.com/media/vendor/awesomplete/js/awesomplete.min.js.map
DevTools failed to parse SourceMap: https://mywebsite.com/media/vendor/css-vars-ponyfill/js/css-vars-ponyfill.min.js.map
DevTools failed to parse SourceMap: https://mywebsite.com/media/vendor/bootstrap/js/bootstrap.bundle.min.js.map

But i have these warnings in every page of Admin.
In frontend i have only this warning:

DevTools failed to parse SourceMap: https://mywebsite.com/media/vendor/bootstrap/js/bootstrap.bundle.min.js.map