private boolean isUnderHome() {
        return this.userDirOrEx.orRethrow().startsWith(this.userHomeOrEx.orRethrow());
    }
Returns {@code true} if {@code userDir} is under {@code userHome}.

<p>Note that the check is performed "literally". It does not take care of the existence of the path.
It does not resolve a symbolic link.
embulk-core/src/main/java/org/embulk/cli/EmbulkSystemPropertiesBuilder.java