Fix NullPointerException when unregistering a map output twice.
Fix NullPointerException when unregistering a map output twice.

huang1900/spark,yanboliang/spark,jrshust/spark,alunarbeach/spark,saturday-shi/spark,rednaxelafx/apache-spark,zzcclp/spark,minixalpha/spark,caneGuy/spark,lyogavin/spark,wzhfy/spark,taroplus/spark,ajaysaini725/spark,huang1900/spark,Aegeaner/spark,saturday-shi/spark,lxsmnv/spark,kimoonkim/spark,cin/spark,rekhajoshm/spark,dotunolafunmiloye/spark,WeichenXu123/spark,jrshust/spark,SnappyDataInc/spark,witgo/spark,ptkool/spark,liutang123/spark,SnappyDataInc/spark,spark-test/spark,shuangshuangwang/spark,xflin/spark,setjet/spark,gioenn/xSpark,tejasapatil/spark,cin/spark,dongjoon-hyun/spark,LantaoJin/spark,jianran/spark,mahak/spark,jiangxb1987/spark,aokolnychyi/spark,alunarbeach/spark,nlalevee/spark,shuangshuangwang/spark,cloud-fan/spark,akopich/spark,saturday-shi/spark,bravo-zhang/spark,minixalpha/spark,sureshthalamati/spark,BryanCutler/spark,bOOm-X/spark,ibm-research-ireland/sparkoscope,ptkool/spark,wzhfy/spark,jiangxb1987/spark,taroplus/spark,bOOm-X/spark,highfei2011/spark,kissmetrics/spark,mahak/spark,darionyaphet/spark,chuckchen/spark,shaneknapp/spark,markhamstra/spark,Aegeaner/spark,ahnqirage/spark,minixalpha/spark,narahari92/spark,kimoonkim/spark,bdrillard/spark,markhamstra/spark,skonto/spark,cloud-fan/spark,ibm-research-ireland/sparkoscope,janewangfb/spark,hvanhovell/spark,patrick-nicholson/spark,ron8hu/spark,szhem/spark,stanzhai/spark,joseph-torres/spark,ueshin/apache-spark,bravo-zhang/spark,poffuomo/spark,metamx/spark,UndeadBaneGitHub/spark,BryanCutler/spark,liyichao/spark,guoxiaolongzte/spark,rezasafi/spark,brad-kaiser/spark,sachintyagi22/spark,icexelloss/spark,sahilTakiar/spark,liyichao/spark,haowu80s/spark,SHASHANKB/spark,dongjoon-hyun/spark,adrian-ionescu/apache-spark,hvanhovell/spark,hvanhovell/spark,rjpower/spark,poffuomo/spark,ConeyLiu/spark,sahilTakiar/spark,vax11780/spark,stanzhai/spark,lvdongr/spark,panfengfeng/spark,aokolnychyi/spark,mike0sv/spark,ioana-delaney/spark,nilsgrabbert/spark,loneknightpy/spark,zero323/spark,xflin/spark,cloud-fan/spark,mahak/spark,witgo/spark,esi-mineset/spark,WindCanDie/spark,xuanyuanking/spark,LantaoJin/spark,zuotingbing/spark,pgandhi999/spark,pgandhi999/spark,highfei2011/spark,rednaxelafx/apache-spark,loneknightpy/spark,mdespriee/spark,saltstar/spark,1haodian/spark,sahilTakiar/spark,guoxiaolongzte/spark,rikima/spark,ddna1021/spark,darionyaphet/spark,map222/spark,wzhfy/spark,tejasapatil/spark,mdespriee/spark,facaiy/spark,cin/spark,gengliangwang/spark,rekhajoshm/spark,skonto/spark,markhamstra/spark,jkbradley/spark,guoxiaolongzte/spark,wangmiao1981/spark,liutang123/spark,michalsenkyr/spark,byakuinss/spark,milliman/spark,bdrillard/spark,yanboliang/spark,minixalpha/spark,dongjoon-hyun/spark,andrewor14/spark,ptkool/spark,metamx/spark,gengliangwang/spark,joseph-torres/spark,lxsmnv/spark,1haodian/spark,wangyum/spark,metamx/spark,sachintyagi22/spark,zzcclp/spark,holdenk/spark,setjet/spark,cloudera/spark,andrewor14/iolap,kissmetrics/spark,dbtsai/spark,holdenk/spark,vinodkc/spark,mzl9039/spark,shaneknapp/spark,apache-spark-on-k8s/spark,dotunolafunmiloye/spark,zero323/spark,maropu/spark,1haodian/spark,hhbyyh/spark,janewangfb/spark,JerryLead/spark,mahak/spark,ueshin/apache-spark,cloudera/spark,eyalfa/spark,mdespriee/spark,stanzhai/spark,goldmedal/spark,cin/spark,hhbyyh/spark,maropu/spark,shubhamchopra/spark,byakuinss/spark,dhruve/spark,shaneknapp/spark,goldmedal/spark,aosagie/spark,huang1900/spark,ConeyLiu/spark,jkbradley/spark,patrick-nicholson/spark,akopich/spark,witgo/spark,dbtsai/spark,andrewor14/spark,JerryLead/spark,sahilTakiar/spark,shubhamchopra/spark,rikima/spark,saturday-shi/spark,publicRoman/spark,sachintyagi22/spark,wgpshashank/spark,big-pegasus/spark,JoshRosen/spark,aray/spark,zzcclp/spark,JerryLead/spark,Aegeaner/spark,kiszk/spark,poffuomo/spark,poffuomo/spark,someorz/spark,bdrillard/spark,shubhamchopra/spark,bravo-zhang/spark,JoshRosen/spark,jlopezmalla/spark,nlalevee/spark,SHASHANKB/spark,SHASHANKB/spark,LantaoJin/spark,JerryLead/spark,hhbyyh/spark,tejasapatil/spark,techaddict/spark,mike0sv/spark,ptkool/spark,saltstar/spark,WindCanDie/spark,kiszk/spark,pgandhi999/spark,spark-test/spark,aray/spark,tejasapatil/spark,rednaxelafx/apache-spark,jianran/spark,alunarbeach/spark,nchammas/spark,ueshin/apache-spark,milliman/spark,1haodian/spark,aokolnychyi/spark,hhbyyh/spark,janewangfb/spark,ibm-research-ireland/sparkoscope,tengpeng/spark,rezasafi/spark,facaiy/spark,eyalfa/spark,jrshust/spark,ioana-delaney/spark,dhruve/spark,liutang123/spark,shuangshuangwang/spark,ibm-research-ireland/sparkoscope,pronix/spark,JoshRosen/spark,kimoonkim/spark,andrewor14/spark,esi-mineset/spark,pgandhi999/spark,tengpeng/spark,bdrillard/spark,cloudera/spark,spark-test/spark,wgpshashank/spark,pgandhi999/spark,narahari92/spark,byakuinss/spark,jrshust/spark,chuckchen/spark,apache/spark,stanzhai/spark,mdespriee/spark,michalsenkyr/spark,ajaysaini725/spark,WindCanDie/spark,kissmetrics/spark,ConeyLiu/spark,pronix/spark,adrian-ionescu/apache-spark,UndeadBaneGitHub/spark,techaddict/spark,yanboliang/spark,1haodian/spark,ibm-research-ireland/sparkoscope,taroplus/spark,guoxiaolongzte/spark,eyalfa/spark,nchammas/spark,caneGuy/spark,1haodian/spark,nilsgrabbert/spark,zuotingbing/spark,eyalfa/spark,techaddict/spark,xuanyuanking/spark,ueshin/apache-spark,kevinyu98/spark,Panos-Bletsos/spark-cost-model-optimizer,koeninger/spark,rikima/spark,ajaysaini725/spark,aosagie/spark,pgandhi999/spark,techaddict/spark,nilsgrabbert/spark,ioana-delaney/spark,debugger87/spark,big-pegasus/spark,apache-spark-on-k8s/spark,rezasafi/spark,xflin/spark,aray/spark,taroplus/spark,ericvandenbergfb/spark,haowu80s/spark,zhouyejoe/spark,zero323/spark,wzhfy/spark,zuotingbing/spark,rekhajoshm/spark,chuckchen/spark,lxsmnv/spark,apache-spark-on-k8s/spark,rekhajoshm/spark,akopich/spark,kissmetrics/spark,kimoonkim/spark,rednaxelafx/apache-spark,saturday-shi/spark,aokolnychyi/spark,tengpeng/spark,rekhajoshm/spark,holdenk/spark,icexelloss/spark,wzhfy/spark,darionyaphet/spark,kimoonkim/spark,metamx/spark,alunarbeach/spark,JoshRosen/spark,brad-kaiser/spark,lvdongr/spark,techaddict/spark,wangyum/spark,xuanyuanking/spark,someorz/spark,jlopezmalla/spark,kevinyu98/spark,ibm-research-ireland/sparkoscope,ueshin/apache-spark,rednaxelafx/apache-spark,michalsenkyr/spark,aokolnychyi/spark,facaiy/spark,sachintyagi22/spark,icexelloss/spark,szhem/spark,WeichenXu123/spark,highfei2011/spark,ahnqirage/spark,icexelloss/spark,wangmiao1981/spark,highfei2011/spark,ueshin/apache-spark,bravo-zhang/spark,koeninger/spark,vinodkc/spark,wgpshashank/spark,xflin/spark,loneknightpy/spark,sachintyagi22/spark,liutang123/spark,lvdongr/spark,apache/spark,caneGuy/spark,apache-spark-on-k8s/spark,LantaoJin/spark,rjpower/spark,kissmetrics/spark,esi-mineset/spark,guoxiaolongzte/spark,minixalpha/spark,adrian-ionescu/apache-spark,andrewor14/iolap,jiangxb1987/spark,ajaysaini725/spark,JoshRosen/spark,ron8hu/spark,ddna1021/spark,sryza/spark,aray/spark,caneGuy/spark,zero323/spark,milliman/spark,vinodkc/spark,tengpeng/spark,wangmiao1981/spark,dongjoon-hyun/spark,actuaryzhang/spark,apache/spark,gioenn/xSpark,sureshthalamati/spark,mzl9039/spark,vinodkc/spark,brad-kaiser/spark,sachintyagi22/spark,kiszk/spark,dhruve/spark,markhamstra/spark,ConeyLiu/spark,metamx/spark,actuaryzhang/spark,andrewor14/spark,holdenk/spark,ConeyLiu/spark,cloud-fan/spark,Panos-Bletsos/spark-cost-model-optimizer,darionyaphet/spark,lxsmnv/spark,someorz/spark,nchammas/spark,kevinyu98/spark,wangmiao1981/spark,rezasafi/spark,koeninger/spark,HyukjinKwon/spark,alunarbeach/spark,akopich/spark,HyukjinKwon/spark,jkbradley/spark,esi-mineset/spark,milliman/spark,setjet/spark,liyichao/spark,Aegeaner/spark,saltstar/spark,rjpower/spark,SHASHANKB/spark,narahari92/spark,szhem/spark,gengliangwang/spark,aosagie/spark,lxsmnv/spark,UndeadBaneGitHub/spark,highfei2011/spark,byakuinss/spark,rikima/spark,loneknightpy/spark,debugger87/spark,ddna1021/spark,tengpeng/spark,ConeyLiu/spark,byakuinss/spark,shuangshuangwang/spark,WindCanDie/spark,mike0sv/spark,bdrillard/spark,markhamstra/spark,HyukjinKwon/spark,patrick-nicholson/spark,liyichao/spark,cloudera/spark,panfengfeng/spark,alunarbeach/spark,huang1900/spark,bOOm-X/spark,publicRoman/spark,jianran/spark,lvdongr/spark,jlopezmalla/spark,chuckchen/spark,SnappyDataInc/spark,hhbyyh/spark,SnappyDataInc/spark,dbtsai/spark,joseph-torres/spark,holdenk/spark,vinodkc/spark,dongjoon-hyun/spark,taroplus/spark,publicRoman/spark,bOOm-X/spark,sureshthalamati/spark,janewangfb/spark,sryza/spark,highfei2011/spark,kiszk/spark,aosagie/spark,ueshin/apache-spark,dhruve/spark,zero323/spark,witgo/spark,rezasafi/spark,poffuomo/spark,MLnick/spark,ioana-delaney/spark,hvanhovell/spark,HyukjinKwon/spark,gengliangwang/spark,ron8hu/spark,ddna1021/spark,Panos-Bletsos/spark-cost-model-optimizer,saltstar/spark,cin/spark,jiangxb1987/spark,highfei2011/spark,gengliangwang/spark,srowen/spark,ptkool/spark,huang1900/spark,srowen/spark,hvanhovell/spark,sahilTakiar/spark,rezasafi/spark,brad-kaiser/spark,yanboliang/spark,aosagie/spark,skonto/spark,milliman/spark,aokolnychyi/spark,szhem/spark,panfengfeng/spark,big-pegasus/spark,chuckchen/spark,haowu80s/spark,ericvandenbergfb/spark,debugger87/spark,saturday-shi/spark,brad-kaiser/spark,stanzhai/spark,UndeadBaneGitHub/spark,yanboliang/spark,mzl9039/spark,BryanCutler/spark,Aegeaner/spark,setjet/spark,kiszk/spark,markhamstra/spark,gioenn/xSpark,MLnick/spark,andrewor14/spark,bdrillard/spark,witgo/spark,ron8hu/spark,vinodkc/spark,dotunolafunmiloye/spark,aray/spark,dbtsai/spark,goldmedal/spark,wgpshashank/spark,patrick-nicholson/spark,shaneknapp/spark,MLnick/spark,goldmedal/spark,andrewor14/iolap,huang1900/spark,jlopezmalla/spark,jlopezmalla/spark,ron8hu/spark,spark-test/spark,gengliangwang/spark,apache-spark-on-k8s/spark,Panos-Bletsos/spark-cost-model-optimizer,dhruve/spark,tengpeng/spark,JoshRosen/spark,apache/spark,joseph-torres/spark,vax11780/spark,patrick-nicholson/spark,map222/spark,eyalfa/spark,wangyum/spark,jkbradley/spark,publicRoman/spark,setjet/spark,jkbradley/spark,someorz/spark,andrewor14/iolap,esi-mineset/spark,dotunolafunmiloye/spark,BryanCutler/spark,shubhamchopra/spark,maropu/spark,andrewor14/spark,spark-test/spark,jianran/spark,zzcclp/spark,zhouyejoe/spark,milliman/spark,saltstar/spark,mahak/spark,sryza/spark,1haodian/spark,bravo-zhang/spark,MLnick/spark,apache-spark-on-k8s/spark,xflin/spark,zuotingbing/spark,goldmedal/spark,wangmiao1981/spark,zhouyejoe/spark,akopich/spark,andrewor14/iolap,actuaryzhang/spark,xuanyuanking/spark,aokolnychyi/spark,wzhfy/spark,patrick-nicholson/spark,caneGuy/spark,zzcclp/spark,zuotingbing/spark,mkolod/incubator-spark,byakuinss/spark,WindCanDie/spark,rednaxelafx/apache-spark,zzcclp/spark,MLnick/spark,ajaysaini725/spark,koeninger/spark,ron8hu/spark,zhouyejoe/spark,shaneknapp/spark,kevinyu98/spark,ddna1021/spark,ptkool/spark,zuotingbing/spark,rezasafi/spark,panfengfeng/spark,tejasapatil/spark,skonto/spark,jiangxb1987/spark,bOOm-X/spark,janewangfb/spark,rekhajoshm/spark,kevinyu98/spark,kissmetrics/spark,xflin/spark,debugger87/spark,gioenn/xSpark,akopich/spark,jkbradley/spark,sryza/spark,LantaoJin/spark,skonto/spark,xflin/spark,facaiy/spark,LantaoJin/spark,mike0sv/spark,haowu80s/spark,loneknightpy/spark,nchammas/spark,ioana-delaney/spark,SHASHANKB/spark,yanboliang/spark,minixalpha/spark,jlopezmalla/spark,witgo/spark,panfengfeng/spark,jianran/spark,jrshust/spark,tengpeng/spark,facaiy/spark,BryanCutler/spark,ptkool/spark,big-pegasus/spark,ahnqirage/spark,srowen/spark,jrshust/spark,techaddict/spark,rikima/spark,brad-kaiser/spark,Panos-Bletsos/spark-cost-model-optimizer,debugger87/spark,UndeadBaneGitHub/spark,haowu80s/spark,wzhfy/spark,srowen/spark,ioana-delaney/spark,nchammas/spark,holdenk/spark,janewangfb/spark,gioenn/xSpark,joseph-torres/spark,icexelloss/spark,lxsmnv/spark,darionyaphet/spark,jrshust/spark,big-pegasus/spark,SnappyDataInc/spark,tejasapatil/spark,mzl9039/spark,HyukjinKwon/spark,UndeadBaneGitHub/spark,akopich/spark,xuanyuanking/spark,lxsmnv/spark,koeninger/spark,wangyum/spark,adrian-ionescu/apache-spark,maropu/spark,sryza/spark,JerryLead/spark,zzcclp/spark,mzl9039/spark,kimoonkim/spark,sureshthalamati/spark,publicRoman/spark,mike0sv/spark,bdrillard/spark,jiangxb1987/spark,hvanhovell/spark,WeichenXu123/spark,mkolod/incubator-spark,nilsgrabbert/spark,dongjoon-hyun/spark,gengliangwang/spark,MLnick/spark,metamx/spark,michalsenkyr/spark,dhruve/spark,wangmiao1981/spark,ahnqirage/spark,saltstar/spark,apache/spark,setjet/spark,map222/spark,holdenk/spark,zero323/spark,ahnqirage/spark,haowu80s/spark,actuaryzhang/spark,vax11780/spark,eyalfa/spark,shubhamchopra/spark,eyalfa/spark,mzl9039/spark,ajaysaini725/spark,markhamstra/spark,ahnqirage/spark,pgandhi999/spark,esi-mineset/spark,zhouyejoe/spark,shubhamchopra/spark,jianran/spark,ericvandenbergfb/spark,rekhajoshm/spark,nilsgrabbert/spark,cin/spark,WindCanDie/spark,jkbradley/spark,shaneknapp/spark,michalsenkyr/spark,ioana-delaney/spark,Panos-Bletsos/spark-cost-model-optimizer,xuanyuanking/spark,chuckchen/spark,techaddict/spark,szhem/spark,mike0sv/spark,Aegeaner/spark,liyichao/spark,maropu/spark,srowen/spark,LantaoJin/spark,shuangshuangwang/spark,map222/spark,ahnqirage/spark,narahari92/spark,milliman/spark,SnappyDataInc/spark,caneGuy/spark,xuanyuanking/spark,srowen/spark,lvdongr/spark,minixalpha/spark,icexelloss/spark,bOOm-X/spark,liyichao/spark,huang1900/spark,nlalevee/spark,big-pegasus/spark,rednaxelafx/apache-spark,zhouyejoe/spark,Panos-Bletsos/spark-cost-model-optimizer,ericvandenbergfb/spark,mike0sv/spark,sureshthalamati/spark,ajaysaini725/spark,matthewfranglen/spark,rjpower/spark,big-pegasus/spark,narahari92/spark,sachintyagi22/spark,patrick-nicholson/spark,zero323/spark,ddna1021/spark,Aegeaner/spark,JoshRosen/spark,aosagie/spark,goldmedal/spark,HyukjinKwon/spark,dhruve/spark,nilsgrabbert/spark,SHASHANKB/spark,zuotingbing/spark,WeichenXu123/spark,joseph-torres/spark,taroplus/spark,mdespriee/spark,guoxiaolongzte/spark,wangmiao1981/spark,HyukjinKwon/spark,panfengfeng/spark,saturday-shi/spark,debugger87/spark,cloudera/spark,poffuomo/spark,dbtsai/spark,pronix/spark,nlalevee/spark,JerryLead/spark,wangyum/spark,kevinyu98/spark,lvdongr/spark,wangyum/spark,ddna1021/spark,lyogavin/spark,gioenn/xSpark,michalsenkyr/spark,spark-test/spark,bravo-zhang/spark,vax11780/spark,publicRoman/spark,witgo/spark,skonto/spark,andrewor14/iolap,someorz/spark,bOOm-X/spark,adrian-ionescu/apache-spark,vinodkc/spark,ron8hu/spark,cloud-fan/spark,byakuinss/spark,map222/spark,lvdongr/spark,apache-spark-on-k8s/spark,shubhamchopra/spark,rikima/spark,liutang123/spark,liutang123/spark,kimoonkim/spark,WeichenXu123/spark,mkolod/incubator-spark,liutang123/spark,srowen/spark,map222/spark,jiangxb1987/spark,mkolod/incubator-spark,kissmetrics/spark,bravo-zhang/spark,loneknightpy/spark,pronix/spark,darionyaphet/spark,pronix/spark,actuaryzhang/spark,alunarbeach/spark,hvanhovell/spark,lyogavin/spark,mdespriee/spark,actuaryzhang/spark,someorz/spark,kiszk/spark,liyichao/spark,janewangfb/spark,chuckchen/spark,szhem/spark,aray/spark,maropu/spark,esi-mineset/spark,nlalevee/spark,apache/spark,kiszk/spark,shuangshuangwang/spark,caneGuy/spark,andrewor14/spark,wangyum/spark,mahak/spark,maropu/spark,dbtsai/spark,ibm-research-ireland/sparkoscope,map222/spark,lyogavin/spark,debugger87/spark,jlopezmalla/spark,hhbyyh/spark,BryanCutler/spark,mkolod/incubator-spark,nchammas/spark,michalsenkyr/spark,dbtsai/spark,nlalevee/spark,dongjoon-hyun/spark,sureshthalamati/spark,andrewor14/iolap,joseph-torres/spark,sahilTakiar/spark,sahilTakiar/spark,icexelloss/spark,publicRoman/spark,adrian-ionescu/apache-spark,apache/spark,stanzhai/spark,facaiy/spark,WindCanDie/spark,shuangshuangwang/spark,facaiy/spark,yanboliang/spark,poffuomo/spark,darionyaphet/spark,kevinyu98/spark,narahari92/spark,zhouyejoe/spark,setjet/spark,goldmedal/spark,cloud-fan/spark,mdespriee/spark,aosagie/spark,sureshthalamati/spark,nilsgrabbert/spark,pronix/spark,someorz/spark,ericvandenbergfb/spark,mzl9039/spark,skonto/spark,guoxiaolongzte/spark,actuaryzhang/spark,szhem/spark,metamx/spark,ericvandenbergfb/spark,MLnick/spark,nlalevee/spark,gioenn/xSpark,ericvandenbergfb/spark,lyogavin/spark,ConeyLiu/spark,SHASHANKB/spark,BryanCutler/spark,hhbyyh/spark,rjpower/spark,brad-kaiser/spark,UndeadBaneGitHub/spark,panfengfeng/spark,adrian-ionescu/apache-spark,shaneknapp/spark,spark-test/spark,jianran/spark,JerryLead/spark,saltstar/spark,taroplus/spark,WeichenXu123/spark,nchammas/spark,loneknightpy/spark,cloud-fan/spark,rikima/spark,WeichenXu123/spark,mahak/spark,stanzhai/spark,SnappyDataInc/spark,cin/spark,tejasapatil/spark,narahari92/spark,aray/spark,vax11780/spark