Test AbstractResultSet::current() to return null on empty array

[samsonasik]

This is based on @rzjack comment at #303 (comment)

Provide a narrative description of what you are trying to accomplish:

• Are you fixing a bug?
• Detail how the bug is invoked currently.
  initialize AbstractResultSet with empty array.
• Detail the original, incorrect behavior.
  The AbstractResultset::current() return [].
• Detail the new, expected behavior.
  The AbstractResultset::current() return null.
• Base your feature on the master branch, and submit against that branch.
• Add a regression test that demonstrates the bug, and proves the fix.
• Add a CHANGELOG.md entry for the fix.

[samsonasik]

@rzjack I can't reproduce issue with the test at AbstractResultSet::current() with initialize with empty array.