Form can’t be empty. You bet. A todas luces.
What is form? One might think about a figure or shape, sometimes human. Well, the Middle Ages are well over in human thinking. Anthropomorphization won’t work in language learning. This is why we might think about using virtual lexical items in our language work.
Some might strongly oppose. ‘Form can’t be empty!’ Right. No doubt about it. Invented words are not totally empty, however. They can have their function for their content.
Psycholinguistic research has showed (Akmajian et al, 1986) that kids can do excellent with invented words. Time and again, they coin words and play with their grammar forms. Invented words help focus on how words work.