in getRenderedTemplate(), the template's optional html message is null-checked before being passed to processText(), however, if it is an empty string an illegalargumentexception will be thrown. This can happen if the xml file defining the template has an empty <htmlMessage> tag, which inserts an empty string into the database, rather than omitting the tag, which inserts a null.

Attached is a simple patch to add an empty string check before processing the html message.