"Project built successfully." but no output at all

[mjaggard]

Bug Description
I auto generated my markdown from OpenAPI v3 using widdershins but when I try to run slate I get nothing in the build directory.
I ran slate successfully using the default index.html.md and got an output, but when I run it with my own index.html.md I get no output at all and "Project built successfully." printed as output, which is patently not true.

Browser (please complete the following information):
N/A

Last upstream Slate commit (run git log --author="\(Robert Lord\)\|\(Matthew Peveler\)\|\(Mike Ralphson\)" | head -n 1):
e5b4d9d

[MasterOdin]

How are you running slate (natively, docker)? Would you be able to share your index.html.md file?