fix empty to null portability in DB2
fix empty to null portability in DB2

drieschel/dbal,adrienbrault/dbal,wuxu92/dbal,kupishkis/dbal,zeroedin-bill/dbal,v-bartusevicius/dbal,mRoca/dbal,mariuz/dbal,arima-ryunosuke/dbal,sarcher/dbal,arima-ryunosuke/dbal,kimhemsoe/dbal,drieschel/dbal,zeroedin-bill/dbal,vortgo/dbal,mihai-stancu/dbal,gencer/dbal,helicon-os/doctrine-dbal,adrienbrault/dbal,mariuz/dbal,mathroc/dbal,shivergard/dbal,mathroc/dbal,webonyx/dbal,shivergard/dbal,PowerKiKi/dbal,sarcher/dbal,cassvail/dbal,mikeSimonson/dbal,nfrignani/dbal,easybiblabs/dbal,kimhemsoe/dbal,v-bartusevicius/dbal,Tobion/dbal,hason/dbal,PowerKiKi/dbal,webonyx/dbal,BenMorel/dbal,arima-ryunosuke/dbal,stchr/dbal,adrienbrault/dbal,deeky666/dbal,easybiblabs/dbal,mikeSimonson/dbal,mariuz/dbal,nfrignani/dbal,vutung2311/dbal,mbeccati/dbal,bspeterson/dbal,hason/dbal,cassvail/dbal,lafourchette/dbal,mihai-stancu/doctrine-dbal,helicon-os/doctrine-dbal,webonyx/dbal,gencer/dbal,vutung2311/dbal,LionwareSolutions/dbal,easybiblabs/dbal,DHager/dbal,PowerKiKi/dbal,mRoca/dbal,kupishkis/dbal,DHager/dbal,mbeccati/dbal,kupishkis/dbal,sarcher/dbal,BenMorel/dbal,lafourchette/dbal,doctrine/dbal,mihai-stancu/dbal,vortgo/dbal,janschoenherr/dbal,wuxu92/dbal,AlexDpy/dbal,AlexDpy/dbal,janschoenherr/dbal,stchr/dbal,stof/dbal,lcobucci/dbal,LionwareSolutions/dbal,deeky666/dbal,stof/dbal,doctrine/dbal,Tobion/dbal,bspeterson/dbal,LionwareSolutions/dbal,mihai-stancu/doctrine-dbal,tk-s/dbal,tk-s/dbal,hason/dbal,lcobucci/dbal