How to define usages of static classes in class diagram

Hello,

I have the following problem. I have to reverse enginere an technical documentation of an existing project. In this proces I entered the moment that i can’t avoid some dirty issues. One of the things I have a trouble to get in an Class Diagram is the usage of static classes, which are only existing static, even on places where it is unnessecery. See the following code:

$Warehouse=FactoryWarehouse::getWarehouse($id)
$Location=FactoryLocation::getLocation($id)
$product="banana";
Stock::Save($Warehouse,$Location,$Banana)

The usage of the Factory Pattern is something I formiler with. But the last line, the Stock-line, is mij problem. In the Stock-class is a lot of things happen, but the only way it is uses is on this way. PHP is very generous in how a programmer can write its code, so the Stock can be there magicly is is never declered before.

How can I make a class diagram of this?

Thank in advance

I normally see static operations in classes illustrated with an underline.
class_static_operation.png