validation allows for nulls and blanks, fixes #76
validation allows for nulls and blanks, fixes #76

laurenancona/Chartbuilder,laurenancona/Chartbuilder,valdobc/volt-teste,zhangweiabc/Chartbuilder,bryceroney/Chartbuilder,NerdWallet/Chartbuilder,Quartz/Chartbuilder,nowthis/Chartbuilder,valdobc/volt-teste,DistilledLtd/Chartbuilder,ajam/Chartbuilder,taylorhxu/Chartbuilder,DistilledLtd/Chartbuilder,Quartz/Chartbuilder,ducroquet/Chartbuilder,ducroquet/Chartbuilder,bwareham/Chartbuilder2,SCPR/Chartbuilder,kway/Chartbuilder,NerdWallet/Chartbuilder,louisstow/Chartbuilder,zhangweiabc/Chartbuilder,smartkarma/Chartbuilder,conversation/Chartbuilder,johnsonchandra/Chartbuilder,correctiv/Chartbuilder,louisstow/Chartbuilder,defenseone/Chartbuilder,taylorhxu/Chartbuilder,nowthis/Chartbuilder,correctiv/Chartbuilder,bryceroney/Chartbuilder,bwareham/Chartbuilder2,kway/Chartbuilder,defenseone/Chartbuilder,ajam/Chartbuilder,SCPR/Chartbuilder,johnsonchandra/Chartbuilder