A mandatory parameter must always be supplied and is written as follows:
SYNTAX
Get-ADUser -Filter <string> ...
In this case, the Filter parameter must be written and it must be given a value. For example, to supply a Filter for the command, the Filter parameter must be explicitly written:
Get-ADUser -Filter { sAMAccountName -eq "SomeName" }
As the parameter, name (Filter) must always be supplied.