In bash, checking for whether an env variable exists uses the -z test,
against a stringified env var, so that the test is actually whether the
env var is empty, but not necessarily undefined. We use this to test
whether JAVA_HOME is set, to determine whether the bundled jdk should be
used. In windows, this test is an actual "undefined" check. This commit
brings the behavior on two systems in sync, opting to allow for an empty
JAVA_HOME in windows to indicate the bundled jdk should be used.
closes#55134
742b69a7dc