Error on build

[dharma66]

Apologies if this turns out to be user error.

I have tried:
cargo install mdbook
mdbook build

on Windows 10, and on Ubuntu 16.04.3 LTS, using master as of the date of this incident. In both cases I get the following error:

$ mdbook build
2018-07-18 07:39:08 [ERROR] (mdbook::utils): Error: Summary parsing failed
2018-07-18 07:39:08 [ERROR] (mdbook::utils): Caused By: There was an error parsing the numbered chapters
2018-07-18 07:39:08 [ERROR] (mdbook::utils): Caused By: Error at line 5, column 16: You can't have an empty link.