Email template

I am doing an HTML email temple and have some questions:

How can I avoid to write the object if that object is not found on the XML?

Example: I call the field “OriginPurchaseOrderItemReference-ID”, and if have no text the email template appears

Referencia cliente: [DeliveryDespatchAdvice-Item-OriginPurchaseOrderItemReference-ID]. I just want it to be empty if there is no reference.