With args/kwagrs signature parsing 's' doesn't handle None as value correctly (sets NoneType object) while with 'z' signature passing None as arg/kwarg value leads to C NULL value.
Coverage remained the same at 90.33% when pulling 0643cd0f4669d0e8c6058b3bb4f746e8fbbbde58 on SantjagoCorkez:None-value-patch into 686fe81e90080ea1781f96e412eef3f4df81994c on mjschultz:master.
With args/kwagrs signature parsing 's' doesn't handle None as value correctly (sets NoneType object) while with 'z' signature passing None as arg/kwarg value leads to C NULL value.