setValueExplicit sets the Value wrongly? to "0" instead of "null"

[Wolfy7]

This is:

- [x] a bug report
- [ ] a feature request
- [ ] **not** a usage question (ask them on https://stackoverflow.com/questions/tagged/phpspreadsheet or https://gitter.im/PHPOffice/PhpSpreadsheet)

What is the expected behavior?

If you want to set the Value explicit to TYPE_Numeric but the value ($pValue) ist "null" the value should be also set to "null".

What is the current behavior?

If a Cell looks like that in the xml-file:
<c r="A1" s="109" t="n" />
the Value for this cell will be set to "0" instead of "null".

What are the steps to reproduce?

If you call setValueExplicit with $pValue = null and $pDataType = DataType::TYPE_NUMERIC the value will be set to "0".

Which versions of PhpSpreadsheet and PHP are affected?

PhpSpeadsheet = 1.18.0 - 2021-05-31
PHP = 7.2.4

Possible solution

Change the line 217 in \src\PhpSpreadsheet\Cell\Cell.php from:

                $this->value = 0 + $pValue;

to

                if(is_null($pValue)){
                    $this->value = null;
                }else{
                    $this->value = 0 + $pValue;
                }

If you want you can assigne this to me and i will provide a PR with this fix.

[MarkBaker]

It does raise the question of why you want to specify type TYPE_NUMERIC with a value of NULL rather than specifying TYPE_NULL

[Wolfy7]

@MarkBaker justified question.
The think is I have (i think) no choice, I have a xlsx-file with some empty cells and in the XML they are defined as mentioned above:

<c r="A1" s="109" t="n" />

So if I read this file in PHPspreadsheet converts this empty cell to "0" cause if the t="n". Maybe the XLSX (XML) file is not "correct" but that's what I don't know.

And also just for my understanding I think if a cell is empty it should stay empty independent of the type. So probably the function should always return empty if the value is null or?

Thanks for your reply.