Use of uninitialized value in substitution (s///) at ./ink2pdf

While running ink2pdf on an inkscape file, I got loads of errors (>100) that all said:
```
Use of uninitialized value in substitution (s///) at ./ink2pdf line [XXX].
```
where XXX is either 343 or 338.
Also, (and I think this is a result of these errors) the generated PDF is just the same page (the first one) over and over again.