Reverts bce64e5

PiperOrigin-RevId: 674083626

xla/python/pytree.cc

@@ -595,9 +595,15 @@ nb::list PyTreeDef::FlattenUpTo(nb::handle xs) const {
 
       case PyTreeKind::kNone:
         if (!object.is_none()) {
-          throw std::invalid_argument(
-              absl::StrFormat("Expected None, got %s.",
-                              nb::cast<std::string_view>(nb::repr(object))));
+          PythonDeprecationWarning(
+              /*stacklevel=*/3,
+              "In a future release of JAX, flatten-up-to will no longer "
+              "consider None to be a tree-prefix of non-None values, got: "
+              "%s.\n\n"
+              "To preserve the current behavior, you can usually write:\n"
+              "  jax.tree.map(lambda x, y: None if x is None else f(x, y), a, "
+              "b, is_leaf=lambda x: x is None)",
+              nb::cast<std::string_view>(nb::repr(object)));
         }
         break;
 

xla/python/xla_client.py

@@ -50,7 +50,7 @@
 
 # Just an internal arbitrary increasing number to help with backward-compatible
 # changes. In JAX, reference this via jax._src.lib.xla_extension_version.
-_version = 284
+_version = 283
 
 # Version number for MLIR:Python components.
 mlir_api_version = 57