What is the default username and password for h2 when there's nothing explicit in JDBC?

Well, duh, that didn't take long.

The answer is -user "".

This might work:

name = "sa"
password = ""

In case you got stuck with the default non-blank user when running the client, the full set of parameters will get you past that:

java -cp <path_to_h2>\h2.jar org.h2.tools.Shell -url "jdbc:h2:file:<jdbc_url>" -driver "org.h2.Driver" -user "" -password ""