This printed things like
```
in function 'f'
called on standard input
in function 'd'
called on standard input
in function 'b'
called on standard input
in function 'a'
called on standard input
```
As a first step, it removes the empty lines so it's now
```
in function 'f'
called on standard input
in function 'd'
called on standard input
in function 'b'
called on standard input
in function 'a'
called on standard input
```
See #5434.