* Use validation classes rather than traits for Statistical functions, and some verification of nullable arguments
* Eliminate more of the issues resolved in phpstan baseline
`Worksheet::getCell()` used to optionnaly return null if passed a
second argument. This second argument was removed entirely and the
method always returns a Cell (possibly creating it if needed).
This make the API more predictable and easier to do static analysis
with tools such as PHPStan.
If you relied on that second parameter, you should instead use the
`Worksheet::cellExists()` before calling `getCell()`.
* Additional unit tests and rationalisation for Financial Functions
* Providing a series of sample files for Financial functions
* Refactor the last of the existing Financial functions
* Some more unit tests with default assignments from null arguments
Co-authored-by: Adrien Crivelli <adrien.crivelli@gmail.com>
Mark Baker
Adrien Crivelli