LGTM.com - false positive - Illegal class 'NoneType' raised

**Description of the false positive**

The type of `MYPY_EX` cannot be `NoneType`:
```python
if t.TYPE_CHECKING or MYPY_EX is None:
[...]
else:
def plugin(version: str) -> t.Type[_NumpyPlugin]:
"""An entry-point for mypy."""
raise MYPY_EX
```

**URL to the alert on the project page on LGTM.com**

https://lgtm.com/projects/g/numpy/numpy/snapshot/6152182e731afcc49e6ff6c657dcd805619bca56/files/numpy/typing/mypy_plugin.py?sort=name&dir=ASC&mode=heatmap#x712afbd0848264dc:1