Resolve default values when a null argument is passed for HLOOKUP(), VLOOKUP() and ADDRESS() functions

[MarkBaker]

This is:

- [X] a bugfix
- [ ] a new feature

Checklist:

• Changes are covered by unit tests
• Code style is respected
• Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• CHANGELOG.md contains a short summary of the change
• Documentation is updated as necessary

Why this change is needed?

When a null value is passed to the HLLOKUP(), VLOOKUP() and ADDRESS() functions for arguments with a default value, then the default wasn't being substituted for the null, which was leading to erroneous behaviour.

This is a fix for Issue #2120