pre upgrade failes with tns_admin home
$ /opt/oracle/ora-dev/products/18.3/db/jdk/bin/java -jar /opt/oracle/ora-dev/products/19.3/db/rdbms/admin/preupgrade.jar FILE TEXT
ERROR - Unexpected error getting TNS_ADMIN home
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$ /opt/oracle/ora-dev/products/18.3/db/jdk/bin/java -jar /opt/oracle/ora-dev/products/19.3/db/rdbms/admin/preupgrade.jar FILE TEXT
ERROR - Unexpected error getting TNS_ADMIN home