PIM-3545 Allow setting values to null/empty in product value setters

| Q                    | A
| -------------------- | ---
| Bug fix?             | Y
| New feature?         | N
| BC breaks?           | N
| CI currently passes? | N
| Tests pass?          | Y
| Scenarios pass?      | running
| Checkstyle issues?*  | N
| PMD issues?**        | N
| Changelog updated?   | N
| Fixed tickets        | ~
| DB schema updated?   | N
| Migration script?    | N
| Doc PR               | ~
You don't need to add null on parameters to call the method with null values. That's my point.
Default parameters are only useful when you don't want to pass all the parameters. That's not the case here