For a bit of background, we use Zend Framework 2 and Doctrine at work. Doctrine will always insert NULL
for values we do not popul
I came across the same problem after a MySQL upgrade. Turns out there is a setting to allow NULL inserts against NOT NULL timestamp fields and get the default value.
explicit_defaults_for_timestamp=0
This is documented at https://dev.mysql.com/doc/refman/5.6/en/server-system-variables.html#sysvar_explicit_defaults_for_timestamp