Coverity found a bug in hamt.c:

** CID 1428443:  Null pointer dereferences  (NULL_RETURNS)
/Python/hamt.c: 1058 in hamt_node_bitmap_without()


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*** CID 1428443:  Null pointer dereferences  (NULL_RETURNS)
/Python/hamt.c: 1058 in hamt_node_bitmap_without()
1052                         assert(hamt_node_collision_count(
1053                                 (PyHamtNode_Collision*)sub_node) > 1);
1054                     }
1055     #endif
1056
1057                     PyHamtNode_Bitmap *clone = hamt_node_bitmap_clone(self);
>>>     CID 1428443:  Null pointer dereferences  (NULL_RETURNS)
>>>     Dereferencing a null pointer "clone".
1058                     Py_SETREF(clone->b_array[val_idx],
1059                               (PyObject *)sub_node);  /* borrow */
1060
1061                     *new_node = (PyHamtNode *)clone;
1062                     return W_NEWNODE;
1063                 }