How to add an empty option to a list?

I have a form with some fields with optional data that comes from a list of options.

I've build a modal with a list of options the user needs to choose that is opened once the user clicks on the field:

The first line (-- null--) is in fact a "NONE OPTION", where the user is choosing none of the options.

This list is used in both situations:

a. The user opens a new form and he clicks on the field, this modal is opened, he clicks in the field to choose a option. He may choose one of the options or decide to quit with no options (he can do it by clicking on the modal close as well)

b. The user has choosen already an option in a previous interaction with the field, but wants to change. He can change to a new option (by choosing it on the list) or he may decide to have no options. At that point, if he clicks on the modal close, he will keep the existing option. So, I've added the "NONE" option (--null--) in order to let him choose none of then and bring the field back to empty.

I'm really in a doubt is this is the correct way to do it and need to grab some ideas on how to "reset" this field. I cannot add buttons to the form, so the solution must be in the modal itself.

Should I keep a text (in example --null--). If so, what would be the best term to use ("None of below", "None", "No option") ? Should I keep an empty line? Any other options?