Why the " unbound variable" error displayed while logging to the server?

Issue

• Issue while logging onto the production host which is Red Hat Enterprise Linux 7.2
• Getting weird error as below :

login as: root
root@test password:
Last login: Thu Apr 21 06:20:59 2016 from test
bash: QT_GRAPHICSSYSTEM_CHECKED: unbound variable
-bash: KSH_VERSION: unbound variable
-bash: PROMPT_COMMAND: unbound variable
root@test - [/root]

• Even re-installing bash rpm also we get the same error. Please assist on this.
• It happens when any user logs on the host.