[CDTOOL-1497] Add Nullable Helper for Int

[rcaril]

Change summary

This PR adds the NullInt func helper to provide the ability to return nil when a int is zero.

All Submissions:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

New Feature Submissions:

• Does your submission pass tests?

=== RUN   TestNullInt
=== PAUSE TestNullInt
=== CONT  TestNullString
=== RUN   TestNullString/non-empty_string_returns_pointer
=== RUN   TestNullString/empty_string_returns_nil
--- PASS: TestNullString (0.00s)
    --- PASS: TestNullString/non-empty_string_returns_pointer (0.00s)
    --- PASS: TestNullString/empty_string_returns_nil (0.00s)
=== CONT  TestNullInt
=== RUN   TestNullInt/non-zero_int_returns_pointer
=== RUN   TestNullInt/zero_returns_nil
--- PASS: TestNullInt (0.00s)
    --- PASS: TestNullInt/non-zero_int_returns_pointer (0.00s)
    --- PASS: TestNullInt/zero_returns_nil (0.00s)
PASS