Add documentation for passing nil to #per
Add documentation for passing nil to #per

kaminari/kaminari,royels/kaminari,peter-umb/umbie_kaminari,yui-knk/kaminari,wkirschbaum/kaminari,wkirschbaum/kaminari,guodongme/kaminari,iberianpig/kaminari,pat/kaminari,danimashu/kaminari,Boomkat/kaminari,bonekost/kaminari,parity/kaminari,sachin21/kaminari,sr-education/kaminari,thiagorp/kaminari,bonekost/kaminari,parity/kaminari,mrhead/kaminari,sendgrid/kaminari,antstorm/kaminari,barkbox/cursor,sr-education/kaminari,bsboris/kaminari,Teino1978-Corp/Teino1978-Corp-kaminari,sendgrid/kaminari,guodongme/kaminari,dblock/kaminari,varvet/kaminari,peter-umb/umbie_kaminari,JuanitoFatas/kaminari,danimashu/kaminari,JuanitoFatas/kaminari,mperrando/kaminari,epicagency/kaminari,plribeiro3000/kaminari,sideci-sample/sideci-sample-kaminari,mrhead/kaminari,jcoyne/kaminari,Zhomart/kaminari,Zhomart/kaminari,mrstif/cursor,sendgrid/kaminari,pat/kaminari,varvet/kaminari,Teino1978-Corp/Teino1978-Corp-kaminari,joe1chen/kaminari,fkagami/kaminari,iberianpig/kaminari,joe1chen/kaminari,sanrodari/kaminari,epicagency/kaminari,jiamaozheng/kaminari,amatsuda/kaminari,royels/kaminari,amatsuda/kaminari,yui-knk/kaminari,aelogica/kaminari,sachin21/kaminari,kaminari/kaminari,antstorm/kaminari,Boomkat/kaminari,onursarikaya/kaminari,dblock/kaminari,plribeiro3000/kaminari,jiamaozheng/kaminari,onursarikaya/kaminari,sanrodari/kaminari,mperrando/kaminari,bsboris/kaminari,thiagorp/kaminari,aelogica/kaminari