WARNING: The HOME variable is not set. Defaulting to a blank string

The HOME variable is set:

PS C:\Users\jshowalter\dev> env | grep HOME
HOMEDRIVE=C:
HOMEPATH=\Users\jshowalter
JAVA_HOME=C:\jdk1.8.0_121
HOME=/c/Users/jshowalter

But when I try to run docker-compose, the first thing it outputs is:

WARNING: The HOME variable is not set. Defaulting to a blank string.

Why is it doing that?