BUG-869: removed useless null check from DataValidationException.checkListKey

Null check is useless because

1. it is already performed in call to overloaded checkListKey
2. value is already dereferenced and if it were null a NullPointerException would have occurred

Expression 'if (isLegal == false)' simplified to 'if (!isLegal)'.

Change-Id: I7bf332e99e35d283726e439caf1d2a39a17df932
Signed-off-by: Martin Vitez <mvitez@cisco.com>
Merge "BUG-869: removed useless null check from DataValidationException.checkListKey"