write value of bitmap as field name

[pjain1]

I was trying to dump bitmaps for a segment and got this error -

Exception in thread "main" java.lang.RuntimeException: java.lang.RuntimeException: com.fasterxml.jackson.core.JsonGenerationException: Can not start an array, expecting field name
	at org.apache.druid.cli.DumpSegment.run(DumpSegment.java:197)
	at org.apache.druid.cli.Main.main(Main.java:112)
Caused by: java.lang.RuntimeException: com.fasterxml.jackson.core.JsonGenerationException: Can not start an array, expecting field name
	at org.apache.druid.cli.DumpSegment$3.apply(DumpSegment.java:391)
	at org.apache.druid.cli.DumpSegment$3.apply(DumpSegment.java:342)
	at org.apache.druid.cli.DumpSegment.withOutputStream(DumpSegment.java:427)
	at org.apache.druid.cli.DumpSegment.runBitmaps(DumpSegment.java:340)
	at org.apache.druid.cli.DumpSegment.run(DumpSegment.java:190)
	... 1 more
Caused by: com.fasterxml.jackson.core.JsonGenerationException: Can not start an array, expecting field name
	at com.fasterxml.jackson.core.JsonGenerator._reportError(JsonGenerator.java:1649)
	at com.fasterxml.jackson.core.json.UTF8JsonGenerator._verifyValueWrite(UTF8JsonGenerator.java:949)
	at com.fasterxml.jackson.core.json.UTF8JsonGenerator.writeStartArray(UTF8JsonGenerator.java:282)
	at org.apache.druid.cli.DumpSegment$3.apply(DumpSegment.java:367)
	... 5 more

So the column value for which bitmap will be output was missing so added it. Not sure how was it working before, can anybody try if they are getting the same exception without this fix ?

[pjain1]

Added one more commit to make sure if null is present in the dictionary then it is respected, without this bitmap for null value will be skipped.

[himanshug]

LGTM
not sure if it could ever work in json writing an array value inside object without writing a field name first. I think it ignores value when field name is not written, in the jackson core version 2.6.7.
do you have 2.6.7 jackson core version or did that get overridden for you by any chance, that could explain why it is failing for you now.

[pjain1]

#5382 downgraded jackson to 2.6.7, probably it was working before this with the higher version.

[clintropolis]

lgtm 👍