It seems that essentially you’re asking if $null values will be added to the array or not. The answer is yes - if you assign an empty or nonexistent variable to an array, then the array element for that position (whatever it should be for that array) will be added to the array with a value of $null. You can see this happen like this:
$a = 1
#$b = 2
$c = 3
$array = @( $a, $b, $c )
The count shows that there are 3 elements in the array, even though echoing the contents of the array only shows the values for $a and $c. So, even though $b has not been assigned a value, it was still accounted for when the array was created. When the shell called $b while creating the array, it found that the value of $b was $null and assigned that value to the array element (the shell follows your instructions exactly, even if your instructions are wrong or don’t make sense).
This is true in general - any time that you call a value that does not exist (variable/array/array element/property/etc), the value is $null. This is something that has to be handled carefully, as it can creep into your script due to a typo (e.g. you have a variable $beta but you referenced $bta instead and now your script is using a value of $null). Your script can continue operating with no obvious problem until the $null value causes something else to fail, which may be difficult to track down when troubleshooting.
Here are some more thorough explanations:
Powershell: Everything you wanted to know about arrays: $null or empty
Powershell: Everything you wanted to know about $null