The Avatica client JAR that we use in the phoenix thin client JAR does not include and sfl4j backend.
This in itself is not a problem, as it allows dependent project to use their preferred backend.
However, we are not adding a backend in the sqlline-thin script either, which results in any log messages being dropped.
We should add a log implementation in the sqlline-thin script to the classpath.
Probably slf4j-simple would be the best choice.