sub! can return nil
sub! can return nil

Revert "drop one more string allocation"

This reverts commit 4d15661d6c46c86a62ee1fc358f4b3ef9dd9f2ea.

pvalena/rails,yhirano55/rails,ledestin/rails,mathieujobin/reduced-rails-for-travis,rails/rails,assain/rails,shioyama/rails,Vasfed/rails,printercu/rails,illacceptanything/illacceptanything,koic/rails,illacceptanything/illacceptanything,hanystudy/rails,yawboakye/rails,rossta/rails,illacceptanything/illacceptanything,mijoharas/rails,fabianoleittes/rails,yalab/rails,rails/rails,Spin42/rails,felipecvo/rails,Sen-Zhang/rails,kmcphillips/rails,fabianoleittes/rails,Envek/rails,maicher/rails,sealocal/rails,Stellenticket/rails,eileencodes/rails,MSP-Greg/rails,ngpestelos/rails,gavingmiller/rails,Edouard-chin/rails,illacceptanything/illacceptanything,printercu/rails,illacceptanything/illacceptanything,yahonda/rails,pschambacher/rails,kenta-s/rails,rails/rails,vipulnsward/rails,utilum/rails,untidy-hair/rails,joonyou/rails,xlymian/rails,yhirano55/rails,koic/rails,prathamesh-sonpatki/rails,illacceptanything/illacceptanything,yhirano55/rails,eileencodes/rails,vipulnsward/rails,kmcphillips/rails,mtsmfm/rails,repinel/rails,shioyama/rails,Envek/rails,joonyou/rails,lucasmazza/rails,gfvcastro/rails,kirs/rails-1,BlakeWilliams/rails,eileencodes/rails,Vasfed/rails,yawboakye/rails,illacceptanything/illacceptanything,rossta/rails,travisofthenorth/rails,tgxworld/rails,illacceptanything/illacceptanything,arjes/rails,voray/rails,assain/rails,odedniv/rails,bolek/rails,Erol/rails,koic/rails,Sen-Zhang/rails,arunagw/rails,kenta-s/rails,mijoharas/rails,sealocal/rails,riseshia/railsguides.kr,coreyward/rails,palkan/rails,marklocklear/rails,yawboakye/rails,vassilevsky/rails,sergey-alekseev/rails,mijoharas/rails,yahonda/rails,schuetzm/rails,flanger001/rails,tgxworld/rails,bogdanvlviv/rails,Edouard-chin/rails,pvalena/rails,kachick/rails,mathieujobin/reduced-rails-for-travis,bradleypriest/rails,brchristian/rails,rbhitchcock/rails,ttanimichi/rails,pvalena/rails,ngpestelos/rails,betesh/rails,vipulnsward/rails,arjes/rails,kddeisz/rails,lcreid/rails,matrinox/rails,joonyou/rails,vipulnsward/rails,amoody2108/TechForJustice,aditya-kapoor/rails,Vasfed/rails,MSP-Greg/rails,yahonda/rails,esparta/rails,voray/rails,travisofthenorth/rails,ttanimichi/rails,kamipo/rails,untidy-hair/rails,bogdanvlviv/rails,gcourtemanche/rails,Stellenticket/rails,printercu/rails,pschambacher/rails,repinel/rails,gavingmiller/rails,esparta/rails,88rabbit/newRails,pvalena/rails,yalab/rails,bogdanvlviv/rails,brchristian/rails,kaspth/rails,notapatch/rails,tjschuck/rails,mechanicles/rails,gavingmiller/rails,fabianoleittes/rails,alecspopa/rails,gfvcastro/rails,rafaelfranca/omg-rails,illacceptanything/illacceptanything,fabianoleittes/rails,utilum/rails,Envek/rails,deraru/rails,voray/rails,Stellenticket/rails,kaspth/rails,betesh/rails,schuetzm/rails,tjschuck/rails,printercu/rails,sergey-alekseev/rails,coreyward/rails,georgeclaghorn/rails,kmayer/rails,bogdanvlviv/rails,baerjam/rails,iainbeeston/rails,BlakeWilliams/rails,illacceptanything/illacceptanything,riseshia/railsguides.kr,elfassy/rails,betesh/rails,mohitnatoo/rails,kaspth/rails,ledestin/rails,yasslab/railsguides.jp,georgeclaghorn/rails,rafaelfranca/omg-rails,illacceptanything/illacceptanything,Spin42/rails,richseviora/rails,Erol/rails,repinel/rails,hanystudy/rails,Spin42/rails,pschambacher/rails,prathamesh-sonpatki/rails,bolek/rails,gcourtemanche/rails,travisofthenorth/rails,mtsmfm/railstest,lcreid/rails,odedniv/rails,matrinox/rails,flanger001/rails,amoody2108/TechForJustice,kmcphillips/rails,utilum/rails,aditya-kapoor/rails,felipecvo/rails,brchristian/rails,xlymian/rails,schuetzm/rails,baerjam/rails,tjschuck/rails,yahonda/rails,richseviora/rails,kirs/rails-1,kachick/rails,shioyama/rails,untidy-hair/rails,samphilipd/rails,kmcphillips/rails,jeremy/rails,baerjam/rails,prathamesh-sonpatki/rails,yasslab/railsguides.jp,mathieujobin/reduced-rails-for-travis,tijwelch/rails,Erol/rails,vassilevsky/rails,yalab/rails,hanystudy/rails,iainbeeston/rails,iainbeeston/rails,jeremy/rails,riseshia/railsguides.kr,palkan/rails,georgeclaghorn/rails,iainbeeston/rails,kamipo/rails,bolek/rails,EmmaB/rails-1,samphilipd/rails,Stellenticket/rails,kenta-s/rails,MichaelSp/rails,vassilevsky/rails,yhirano55/rails,kirs/rails-1,lucasmazza/rails,MSP-Greg/rails,lcreid/rails,kamipo/rails,Erol/rails,MichaelSp/rails,tijwelch/rails,ledestin/rails,Edouard-chin/rails,mohitnatoo/rails,jeremy/rails,schuetzm/rails,notapatch/rails,notapatch/rails,richseviora/rails,EmmaB/rails-1,lcreid/rails,tgxworld/rails,tjschuck/rails,88rabbit/newRails,bradleypriest/rails,lucasmazza/rails,flanger001/rails,gcourtemanche/rails,starknx/rails,mtsmfm/railstest,kachick/rails,shioyama/rails,Vasfed/rails,assain/rails,kmayer/rails,MSP-Greg/rails,gfvcastro/rails,georgeclaghorn/rails,matrinox/rails,ttanimichi/rails,travisofthenorth/rails,mtsmfm/rails,marklocklear/rails,xlymian/rails,yasslab/railsguides.jp,rafaelfranca/omg-rails,eileencodes/rails,joonyou/rails,Envek/rails,palkan/rails,Edouard-chin/rails,starknx/rails,kmayer/rails,maicher/rails,BlakeWilliams/rails,alecspopa/rails,arunagw/rails,EmmaB/rails-1,jeremy/rails,tijwelch/rails,gfvcastro/rails,mechanicles/rails,arjes/rails,ngpestelos/rails,kddeisz/rails,illacceptanything/illacceptanything,notapatch/rails,stefanmb/rails,samphilipd/rails,illacceptanything/illacceptanything,deraru/rails,mohitnatoo/rails,utilum/rails,riseshia/railsguides.kr,flanger001/rails,mechanicles/rails,aditya-kapoor/rails,tgxworld/rails,starknx/rails,marklocklear/rails,MichaelSp/rails,elfassy/rails,gauravtiwari/rails,aditya-kapoor/rails,yasslab/railsguides.jp,bradleypriest/rails,kddeisz/rails,arunagw/rails,amoody2108/TechForJustice,mtsmfm/rails,rbhitchcock/rails,palkan/rails,sealocal/rails,stefanmb/rails,yalab/rails,kddeisz/rails,BlakeWilliams/rails,gauravtiwari/rails,untidy-hair/rails,maicher/rails,gauravtiwari/rails,mechanicles/rails,88rabbit/newRails,rossta/rails,stefanmb/rails,Sen-Zhang/rails,deraru/rails,illacceptanything/illacceptanything,repinel/rails,esparta/rails,alecspopa/rails,rbhitchcock/rails,prathamesh-sonpatki/rails,illacceptanything/illacceptanything,mtsmfm/railstest,elfassy/rails,baerjam/rails,odedniv/rails,betesh/rails,deraru/rails,felipecvo/rails,yawboakye/rails,arunagw/rails,esparta/rails,rails/rails,mohitnatoo/rails,sergey-alekseev/rails,coreyward/rails,assain/rails