After googling I read through Tim Hunt & Joseph Rézeau's discussion on this topic, though it's closed now and I'm still puzzled...
Using Moodle 3.7.3
After importing questions in gift format, when previewing a quiz I had a blank answer in the dropdown for a matching question. Opening the question, I found < typed into the option that looked blank. (Its a simple match the correct symbol to each definition question for primary learners). I tried putting a backslash before the symbol like for special characters before importing gift, then the html format suggested in the old post, but neither worked. As with these two tries, when I just put < again, Moodle wouldn't let me save the question, saying a value is needed in the field.