There is nothing at the foundation of existence.
Fortunately, there is more to existence than that trauma informed meaning.
Sartre’s philosophical myopia, at least the more narrow “Existentialism” part, was brought about by the incredible trauma that the world was encountering in the early 20th century. He could only see through correlation.
And, remembering Kierkegaard, but not in Sartre’s way, just because we are heirs to a particular existential state, does not mean we must be limited by it: nothing is a result of making meaning, not the ground of it.
The result of Sartre’s nothingness is incorrect.
This is to say: Something is the result of meaning making. Nothing is always informing what something is able be.