[Question] behavior of `null + null = 0`

[tyamahori <tyamahori@xxxxxxxxx>]

Dear PHP users.

I have questions about the behavior `null + null = 0`.

Since PHP4.3.0, `null + null` becomes `0`.

https://3v4l.org/YX3Od#veol

Form php-src, 

https://github.com/php/php-src/blob/e2189e5f376092eeaeb4c06ff9b5918bfc016917/Zend/zend_operators.c#L325

It seems _zendi_try_convert_scalar_to_number converts null to 0.

Do you know who decided this behavior ? 

Do you know how did this behavior come about? 

Regards.

Kazuki