models: fix slice creation (#1130)
models: fix slice creation (#1130)

Fix #1128
mistercrunch/panoramix,airbnb/caravel,massgov/incubator-superset,jeromecn/caravel_viz_full,FrederichCheng/incubator-superset,zhouyao1994/incubator-superset,francisliyy/caravel-aidp,wbsljh/caravel,timifasubaa/incubator-superset,airbnb/caravel,jeromecn/caravel_viz_full,robert-digit/superset,ArijanaBrlek/superset,alanmcruickshank/superset-dev,robert-digit/superset,apache/incubator-superset,massgov/incubator-superset,timifasubaa/incubator-superset,wbsljh/caravel-aidp,BRD-CD/superset,apache/incubator-superset,nekia/incubator-superset-dev,timifasubaa/incubator-superset,jeromecn/caravel_viz_full,mistercrunch/panoramix,ArijanaBrlek/superset,francisliyy/caravel-aidp,massgov/incubator-superset,zhouyao1994/incubator-superset,airbnb/superset,wbsljh/caravel,asdf2014/superset,airbnb/superset,BRD-CD/superset,zhouyao1994/incubator-superset,wbsljh/caravel,BRD-CD/superset,nekia/incubator-superset-dev,apache/incubator-superset,apache/incubator-superset,asdf2014/superset,nekia/incubator-superset-dev,airbnb/caravel,dmigo/incubator-superset,alanmcruickshank/superset-dev,SingTel-DataCo/incubator-superset,apache/incubator-superset,dmigo/incubator-superset,wbsljh/caravel-aidp,nekia/incubator-superset-dev,wbsljh/caravel-aidp,alanmcruickshank/superset-dev,massgov/incubator-superset,alanmcruickshank/superset-dev,robert-digit/superset,SingTel-DataCo/incubator-superset,FrederichCheng/incubator-superset,asdf2014/superset,francisliyy/caravel-aidp,BRD-CD/superset,FrederichCheng/incubator-superset,zhouyao1994/incubator-superset,ArijanaBrlek/superset,dmigo/incubator-superset,robert-digit/superset,mistercrunch/panoramix,ArijanaBrlek/superset,zhouyao1994/incubator-superset,airbnb/superset,mistercrunch/panoramix,timifasubaa/incubator-superset,airbnb/superset,wbsljh/caravel-aidp,SingTel-DataCo/incubator-superset,wbsljh/caravel,asdf2014/superset,airbnb/caravel,dmigo/incubator-superset,SingTel-DataCo/incubator-superset,jeromecn/caravel_viz_full,francisliyy/caravel-aidp,FrederichCheng/incubator-superset