replace NULL with nullptr

git-svn-id: https://svn.code.sf.net/p/moneymanagerex/code/trunk@6547 7f5d68d0-c712-0410-839f-9b116a576cc5
use explicit

git-svn-id: https://svn.code.sf.net/p/moneymanagerex/code/trunk@6548 7f5d68d0-c712-0410-839f-9b116a576cc5
explicit to prevent human error

git-svn-id: https://svn.code.sf.net/p/moneymanagerex/code/trunk@6549 7f5d68d0-c712-0410-839f-9b116a576cc5
assign operator

git-svn-id: https://svn.code.sf.net/p/moneymanagerex/code/trunk@6550 7f5d68d0-c712-0410-839f-9b116a576cc5
assign operator

git-svn-id: https://svn.code.sf.net/p/moneymanagerex/code/trunk@6551 7f5d68d0-c712-0410-839f-9b116a576cc5
in-place update

git-svn-id: https://svn.code.sf.net/p/moneymanagerex/code/trunk@6552 7f5d68d0-c712-0410-839f-9b116a576cc5