How to both omit empty xml ports, and be able to set a string to "" ?

[doisyg]

So this options is great! It allows to not define a specific port of a specific node instance. And hence have getInput return to false in the code. Our use case there: when mapping to a ros action, to not set the corresponding goal field, and hence fall back to the default value defined in the ros action definition without having the BT context needing to know about what should be the default value.

However, there are cases when we want to explicitly set a port value to an empty string "" in the BT. And it doesn't seem possible with the option above set (saving a BT in Groot with a port value of "" deletes it). Is there a special character that could be used in Groot as an explicit empty string ?
(workaround is to define and use {empty_string})