Resolve Error: “The template cannot be saved due to the following errors: The following has evaluated to null or missing.” When Customizing a System Email Template

Scenario

User customizes a system email template and an error alert is returned.

The behavior is caused by some system email templates referencing record types that are only available when their underlying features are enabled. For example, if the Gift Certificates feature is disabled, the native Standard Web Site Gift Certificate system email template would not be able to reference data from gift certificate records. Subsequently, customizing the template would return the error alert.

The solution is to enable the underlying feature.

Solution

1. Navigate to Setup > Company > Enable Features
2. Feature: Enter Checkmark 
3. Click Save

Further, the Standard Case Escalation Notification template references issue records, thus may require the Issue Management feature to be enabled. If enabling the feature is not available, you may either follow the below steps, or contact your account manager to help make the feature available for the account.

1. Navigate to Setup > Company > System Email Templates
2. Standard Case Escalation Notification: Click Customize
3. Name: Enter name
4. Text Editor: Click Source button
5. Scroll down to line 77
6. Replace <#list issue.history as history> with <#list case.history as history>
7. Click Save