Allow sending email with an "empty" template model.

[atheken]

The send with template endpoint requires a template model to be passed when sending a message. However, an "empty" model is OK to use if the template doesn't require any data from the user when sending. Postmark-PHP appears to be filtering this 'empty' model out, when sending it to the server, causing an error.

[hwmatthewa]

Can confirm. Had to workaround this by passing in faux data.