ConvertFrom-Json "add" null items to array - json

Question

I am working with a file that has a JSON string in it.
{
"ConfigurationItems": [{
"ActiveDirectory": [{
"Users": [
{ "FirstName": "U1", "LastName": "L1", "Department": "D1", "UserName": "UN1" },
{ "FirstName": "U2", "LastName": "L2", "Department": "D2", "UserName": "UN2" },
{ "FirstName": "U3", "LastName": "L3", "Department": "D3", "UserName": "UN3" },
{ "FirstName": "U4", "LastName": "L4", "Department": "D4", "UserName": "UN4" },
{ "FirstName": "U5", "LastName": "L5", "Department": "D5", "UserName": "UN5" }
]
},
{
"Groups": [
{ "Name": "G1", "Scope": "Global" },
{ "Name": "G2", "Scope": "Global" },
{ "Name": "G3", "Scope": "Global" }
]
},
{
"OU": [
{ "Name": "N1" },
{ "Name": "N2" },
{ "Name": "N3" }
]
}
]
}]
}
I assign this to a variable by doing the following:
$t = Get-content -path $pathtoJSON -raw | ConvertFrom-Json
Now comes the part I cannot explain if I get the count of Users it returns 7
$t.ConfigurationItems.ActiveDirectory.Users.Count
The main issue is when I iterate through this, I will always end up with two $null items in my loop, which throws off my code. How do I ensure I get the correct count from ConvertFrom-Json. For the time being I have worked around this by checking if my array item is not $null
I am using PS 5.1 for this.