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### Description

The Python3 modules violate Python's exception handling contract.

<!-- Explain what you did, what you expected to happen, and what actually happened. -->

### Troubleshooting

#### Reproduction

``` KSR.pc.sets("$fU",None) ```

#### Debugging Data

``` Unhandled exception in the Python code: TypeError: kemi-param-ss() argument 2 must be str, not None

The above exception was the direct cause of the following exception:

Traceback (most recent call last): File "/usr/local/lib/python3.11/dist-packages/kamailio/trace.py", line 212, in pac return proc(*a, **k) ^^^^^^^^^^^^^ File "/usr/local/lib/python3.11/dist-packages/kamailio/_basic.py", line 181, in ksr_request_route self.do_route(msg) File "/usr/local/lib/python3.11/dist-packages/kamailio/_basic.py", line 261, in do_route self.route_static(msg) File "/usr/local/lib/python3.11/dist-packages/kamailio/_basic.py", line 287, in route_static if self.fix_addrs(msg): ^^^^^^^^^^^^^^^^^^^ File "/usr/local/lib/python3.11/dist-packages/kamailio/_basic.py", line 334, in fix_addrs PV.tU = dnr ^^^^^ File "/usr/local/lib/python3.11/dist-packages/kamailio/var.py", line 46, in __setattr__ return self.__setitem__(k, v) ^^^^^^^^^^^^^^^^^^^^^^ File "/usr/local/lib/python3.11/dist-packages/kamailio/var.py", line 73, in __setitem__ KSR.pv.sets("$fU", v) SystemError: <built-in function sets> returned a result with an exception set ```

### Possible Solutions

See PR #4044

### Additional Information

* **Kamailio Version** - output of `kamailio -v`

``` seen with 5.6 and 5.8 ```

* **Operating System**:

Debian Stable but doesn't matter