ARROW-2214: [JS] add nullBitmap getter to DictionaryData that proxies to its indices' nullBitmap
ARROW-2214: [JS] add nullBitmap getter to DictionaryData that proxies to its indices' nullBitmap

Resolves https://issues.apache.org/jira/browse/ARROW-2214

Author: Paul Taylor <paul.e.taylor@me.com>

Closes #1659 from trxcllnt/ARROW-2214 and squashes the following commits:

8c4ba46 <Paul Taylor> add nullBitmap getter to DictionaryData that proxies to its indices' nullBitmap

wesm/arrow,xhochy/arrow,yufeldman/arrow,pcmoritz/arrow,tebeka/arrow,laurentgo/arrow,laurentgo/arrow,icexelloss/arrow,itaiin/arrow,xhochy/arrow,renesugar/arrow,apache/arrow,wagavulin/arrow,wagavulin/arrow,apache/arrow,pcmoritz/arrow,tebeka/arrow,renesugar/arrow,xhochy/arrow,apache/arrow,pcmoritz/arrow,laurentgo/arrow,pcmoritz/arrow,tebeka/arrow,cpcloud/arrow,pcmoritz/arrow,laurentgo/arrow,yufeldman/arrow,majetideepak/arrow,itaiin/arrow,xhochy/arrow,wesm/arrow,laurentgo/arrow,majetideepak/arrow,renesugar/arrow,icexelloss/arrow,icexelloss/arrow,renesugar/arrow,tebeka/arrow,pcmoritz/arrow,wesm/arrow,apache/arrow,pcmoritz/arrow,laurentgo/arrow,icexelloss/arrow,renesugar/arrow,pcmoritz/arrow,kou/arrow,laurentgo/arrow,icexelloss/arrow,kou/arrow,kou/arrow,majetideepak/arrow,wagavulin/arrow,apache/arrow,cpcloud/arrow,apache/arrow,dremio/arrow,cpcloud/arrow,renesugar/arrow,apache/arrow,wesm/arrow,tebeka/arrow,renesugar/arrow,cpcloud/arrow,cpcloud/arrow,renesugar/arrow,itaiin/arrow,pcmoritz/arrow,yufeldman/arrow,laurentgo/arrow,wesm/arrow,itaiin/arrow,itaiin/arrow,xhochy/arrow,tebeka/arrow,pcmoritz/arrow,xhochy/arrow,yufeldman/arrow,cpcloud/arrow,majetideepak/arrow,wesm/arrow,apache/arrow,kou/arrow,kou/arrow,cpcloud/arrow,yufeldman/arrow,pcmoritz/arrow,majetideepak/arrow,wesm/arrow,kou/arrow,laurentgo/arrow,wagavulin/arrow,xhochy/arrow,majetideepak/arrow,renesugar/arrow,xhochy/arrow,icexelloss/arrow,tebeka/arrow,cpcloud/arrow,tebeka/arrow,laurentgo/arrow,pcmoritz/arrow,yufeldman/arrow,apache/arrow,dremio/arrow,itaiin/arrow,renesugar/arrow,xhochy/arrow,tebeka/arrow,icexelloss/arrow,kou/arrow,dremio/arrow,xhochy/arrow,itaiin/arrow,renesugar/arrow,wesm/arrow,icexelloss/arrow,dremio/arrow,wagavulin/arrow,icexelloss/arrow,kou/arrow,wagavulin/arrow,wagavulin/arrow,dremio/arrow,apache/arrow,yufeldman/arrow,laurentgo/arrow,majetideepak/arrow,xhochy/arrow,wagavulin/arrow,itaiin/arrow,wagavulin/arrow,wesm/arrow,cpcloud/arrow,dremio/arrow,xhochy/arrow,majetideepak/arrow,yufeldman/arrow,cpcloud/arrow,majetideepak/arrow,majetideepak/arrow,yufeldman/arrow,renesugar/arrow,wesm/arrow,itaiin/arrow,wagavulin/arrow,pcmoritz/arrow,apache/arrow,xhochy/arrow,apache/arrow,itaiin/arrow,pcmoritz/arrow,kou/arrow,kou/arrow,xhochy/arrow,dremio/arrow,renesugar/arrow,wesm/arrow,majetideepak/arrow,itaiin/arrow,wagavulin/arrow,wesm/arrow,cpcloud/arrow,icexelloss/arrow,dremio/arrow,majetideepak/arrow,wagavulin/arrow,icexelloss/arrow,laurentgo/arrow,cpcloud/arrow,yufeldman/arrow,apache/arrow,itaiin/arrow,icexelloss/arrow,cpcloud/arrow,icexelloss/arrow,kou/arrow,dremio/arrow,pcmoritz/arrow,itaiin/arrow,renesugar/arrow,cpcloud/arrow,icexelloss/arrow,renesugar/arrow,xhochy/arrow,kou/arrow,itaiin/arrow,dremio/arrow,tebeka/arrow,wesm/arrow,kou/arrow,laurentgo/arrow,kou/arrow,apache/arrow,majetideepak/arrow,yufeldman/arrow,dremio/arrow,wesm/arrow,laurentgo/arrow,laurentgo/arrow,majetideepak/arrow,majetideepak/arrow,itaiin/arrow