```python
def format_stack_entry(self, frame_lineno, lprefix=': '):
...
frame, lineno = frame_lineno
```
The type of `frame_lineno` is `tuple[FrameType, int]` not `int`,
understandably, since the type of `frame_lineno` can be interprted as
the line number of the frame. But looking at the implementation of
`Bdb.format_stack_entry`, it is clear that `frame_lineno` is a tuple.
It is also necessary to somehow pass a frame to `format_stack_entry` if
we want it to be formatted...
From the source it expects that the second parameter (conversion), can
be None:
```python
def convert_field(self, value, conversion):
# do any conversion on the resulting object
if conversion is None:
return value
...
```
Since at least 17 years according to git blame, as None is refered as
early as 11529195cae2438a3ac003babcb1b11af67c4037
And still present in main branch:
https://github.com/python/cpython/blob/ef3ceab09d2d0959c343c662461123d5b0e0b64b/Lib/string.py
M Bussonnier