D5W1A1 RNN Backward pass - uninitialized cache unpacked

RNN_backward test case caches (caches_tmp) not initialized. So when the function unpacks, I get an error

(caches, x) = caches
(a1, a0, x1, parameters) = caches[0]

cannot unpack non-iterable NoneType object

Please share your full error. It is very likely the mistake is in your code, not with the test case. You have to replace all the None with correct code.

Your first line is incorrect. Where is the variable caches on the RHS of that assignment statement defined?