$null In Powershell

Kevin Marquette goes into great detail on Powershell’s $nullconcept:

When a $null value is used in a numeric equation then your results will be invalid if they don’t give an error. Sometimes the $null will evaluate to 0 and other times it will make the whole result $null. Here is an example with multiplication that gives 0 or $nulldepending on the order of the values.

Nulls are tricky to handle in any language, making their nuances important to understand.