Check for null when getting DTV values (JDBC spec compliance - getBinaryStream /getAsciiStream will return null when the value is null)

[machavan]

This fix of checking for null value of a DTVImpl before calling DTVImpl::getValue has shown some perf gains in our internal benchmark.

This fix will change behavior of getBinaryStream /getAsciiStream in ResultSet to be compliant with JDBC specs:
a Java input stream that delivers the database column value as a stream of one-byte ASCII characters; if the value is SQL NULL, the value returned is null

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.33%. Comparing base (e63814e) to head (01e79e9).
Report is 3 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2600      +/-   ##
============================================
- Coverage     51.35%   51.33%   -0.03%     
+ Complexity     3981     3970      -11     
============================================
  Files           147      147              
  Lines         33686    33688       +2     
  Branches       5627     5628       +1     
============================================
- Hits          17300    17294       -6     
+ Misses        13956    13953       -3     
- Partials       2430     2441      +11     

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[lilgreenbird]

add test?

[muskan124947]

Ado pipeline : https://sqlclientdrivers.visualstudio.com/mssql-jdbc/_build/results?buildId=108714&view=results

[machavan]

add test?

Verified that existing tests already cover this code path. This code path is hit for any get call on a ResultSet that returns NULL. e.g. many tests in ResultSetTest cover this.

Addressed

[lilgreenbird]

test added in PR #2617