Due to a bug in JAX, JAX previously permitted `jax.tree.map(f, None, x)` where `x` is not `None`, effectively treating `None` as if it were pytree-prefix of any value. But `None` is a pytree container, and it is only a prefix of `None` itself.
Fix code that was relying on this bug. Most commonly, the fix is to write
`jax.tree.map(lambda a, b: (None if a is None else f(a, b)), x, y, is_leaf=lambda t: t is None)`.
PiperOrigin-RevId: 673258116
808003b4e2