"This value should be of the correct primitive type." error saving node

I debugged my way into PrimitiveTypeConstraint::validate() to see what was going on.

I found that the field value of "1976-01-01T05:00:00" is returning the error "The timestamp must be numeric." Which makes sense.

While looking at the tests for the datetime_datelist_no_time field widget I realized that there isn't any test coverage for the field to make sure the data saves correctly.

I think this was a mixup on my end, once I recreated the field as a datetime field with the date-only option on the field the field widget worked correctly.