why doesn't the _aexit_ function have a check if self._kernel is None?

[brando90]

when the coq serapi instance is one if its fields can be None:

    def __init__(self, kernel_or_cfg: Union[pycoq.kernel.LocalKernel, pycoq.common.LocalKernelConfig], logfname=None):
        """ 
        wraps coq-serapi interface on the running kernel object
        """
        self._logfname = logfname
        if isinstance(kernel_or_cfg, pycoq.kernel.LocalKernel):
            self._kernel = kernel_or_cfg
            self._cfg = None
        elif isinstance(kernel_or_cfg, pycoq.common.LocalKernelConfig):
            self._kernel = None
            self._cfg = kernel_or_cfg
        else:
            raise TypeError("CoqSerapi class must be initialized either with an existing kernel "
                            "object of type pycoq.kernel.LocalKernel or config object of type "
                            " pycoq.common.LocalKernelConfig "
                            f"but the supplied argument has type {type(kernel_or_cfg)}")

but a exist there is not check that we use the one is not None

    async def __aexit__(self, exception_type, exception_value, traceback):
        await self._kernel.__aexit__(exception_type, exception_value, traceback)
        async for line in self._kernel.readlines():
            self._serapi_response_history.append(line)
...

why?

also what resources is it trying to let go? @pestun