redhat-upgrade-tool failed with a python traceback and a error "grubby: kernel not found" in Red Hat Enterprise Linux 6

Issue

redhat-upgrade-tool failed with the following error.

grubby: kernel not found
Traceback (most recent call last):
  File "/usr/bin/redhat-upgrade-tool", line 448, in <module>
    main(args)
  File "/usr/bin/redhat-upgrade-tool", line 369, in main
    upgrade_boot_args()
  File "/usr/lib/python2.6/site-packages/redhat_upgrade_tool/boot.py", line 138, in upgrade_boot_args
    kinfo = check_output(['grubby', '--info=%s' % kernel]).split('\n')
  File "/usr/lib/python2.6/site-packages/redhat_upgrade_tool/util.py", line 50, in check_output
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['grubby', '--info=']' returned non-zero exit status 1