neovim/neovim — pull request #1471 by splinterofchaos (2014-11-14 00:25:27+00:00)
Title: jobstart: Check prg arguments for NULL.

So, this segfaults:
```vim
new
call jobstart('', 'echo', [expand('')])
```
Sometimes, vim uses `NULL` to represent an empty string--not always, but apparently `expand('')` (which will always be empty in a new buffer) does. `get_string_tv()` protects against this.