[Java] optimize null count when serializing vectors.

[asfimport]

nulls are stored in bits. We should be able to use more efficient ways to count nulls:

arrow/java/vector/src/main/java/org/apache/arrow/vector/VectorUnloader.java

Line 68 in 6996c17

nullCount ++;

Reporter: Julien Le Dem / @julienledem
Assignee: Mohamed Zenadi / @zeapo

_{Note: This issue was originally created as ARROW-380. Please see the migration documentation for further details.}

[asfimport]

Julien Le Dem / @julienledem:
@zeapo yes.
possibly getNullCount() ?

[asfimport]

Mohamed Zenadi / @zeapo:
The PR : #207

[asfimport]

Mohamed Zenadi / @zeapo:
Could you check if it's mergeable?

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 207
#207