Email Bounced Soft With Details 'Empty address: []'

Issue Description
An email was sent to leads but immediately returned an 'Email Bounced Soft' Activity Type with the Activity Details stating: 'Details: Empty address: []'

Issue Resolution
This is due to a token used in the 'From Address' Field in the Email editor that does not have a valid value or valid default value.

For example: {{lead.Partner Email:default=edit me}}
The Record's field value for 'Partner Email' is Empty.

As there is no value for the record the token would use the default value 'edit me' which is not a valid value. A valid value must be an email string format such as mark@eto.com