Void Parameter In array_keys()¶
There is a ‘void’ parameter in PHP. It is the second argument of array_keys().
That second parameter is often omitted (and unknown).
If present, it is typed ‘mixed’ to allow any value to be searched (here, null).
If absent, array_keys() returns ALL keys. When absent, it is not null, nor any other type. The last one possible is ‘void’
Type is then : void|mixed.
