I am trying to include a conditional logic in my custom Email Template, which includes merge fields.
When I include the following formula in my template:

<br />• Case #: {!IF(Case.RecordType ="Enterprise", {!Case.CaseNumber}, "not enterprise")}

The output in my email template looks as follows:

Case #: , "not enterprise")}

And when I edit the Email Template again, I can see that my code had changed to the following:

<br />• Case #: {!NullValue(IF(Case.RecordType ="Enterprise", "{!Case.CaseNumber")}, "not enterprise")}

Why is that?