Using OpenActivities or ActivityHistory metadata types results in an Error when the Position Date field value is NULL

[deejay-hub]

Time Warp version
1.10

Describe the bug
When you activate the custom metadata type corresponding to OpenActivities or ActivityHistory you can get an error if the date used returns a null value. Since the default value is ActivityDate (Due Date) there are many tasks where this value could be null

To reproduce
Activate OpenActivities under Account. Create a task with a blank Due Date.

You now get an error.

Expected behaviour
For OpenActivities and ActivityHistory when the Position Date field value is null it should ignore that record and not plot it.