Cannot index into a null array?

Pete Long
Pete Long used Ask the Experts™
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Hi

Ive got this

#Create NIC (called MyNicName)
$nicName = "myNicName"
$nic = New-AzureRmNetworkInterface -Name $nicName `
   -ResourceGroupName $rgName `
   -Location $location -SubnetId $azvnetworks.Subnets[0].Id `
   -PublicIpAddressId $pip.Id `
   -NetworkSecurityGroupId $aznsg.Id

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However when I run it I get

Cannot index into a null array.
At line:1 char:1
+ $nic = New-AzureRmNetworkInterface -Name $nicName `
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : NullArray

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That means nothing to me (sorry)

What have I done wrong?

Pete
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Chinmay PatelChief Technology Ninja
Distinguished Expert 2018

Commented:
Hi Pete,

Any decent programming language will not let you perform operation with a null object.
$azvnetworks.Subnets[0].Id
You see [0] (square brackets and a number within), it is a way for programming language to inspect members of an array.

I think your variable, $azvnetworks.Subnets is not populated with a value and as it is a null indexing operation cannot be performed and hence the error.

How are you getting $azvnetworks? Can you share the complete script?

Regards,
Chinmay.
nociSoftware Engineer
Distinguished Expert 2018

Commented:
Here is an array: $azvnetworks.Subnets[0].Id
where you want element 0, (using index 0).
If the array is empty then there are no elements at all so trying to get one will fail.

First check if $azvnetworks.Subnets does hold data before using it.
Pete LongTechnical Consultant

Author

Commented:
Thank guys

I'm using these instructions

https://docs.microsoft.com/en-us/azure/virtual-machines/windows/create-vm-specialized

On THAT example that string is called $vnet

in my example its called $azvnetworks

Which I populated earlier by doing this;
$azvnetworks = Read-Host -Prompt 'Enter Virtual Netwotk NAME (from above);'

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Pete
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Pete LongTechnical Consultant

Author

Commented:
Ah OK I think I see the problem that is populated with this

$vnet = New-AzureRmVirtualNetwork `
   -Name $vnetName -ResourceGroupName $destinationResourceGroup `
   -Location $location `
   -AddressPrefix 10.0.0.0/16 `
   -Subnet $singleSubnet

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I dont need to create one because I already have one!! (called Main-LAN)

PowerCLI C:\Program Files (x86)\VMware\Infrastructure\vSphere PowerCLI> Get-AzureRmVirtualNetwork
WARNING: Breaking changes in the cmdlet 'Get-AzureRmVirtualNetwork' :
WARNING:  - "The output type 'Microsoft.Azure.Commands.Network.Models.PSVirtualNetwork' is changing"
 - The following properties in the output type are being deprecated :
 'EnableVmProtection'


ResourceGroupName Name     Location ProvisioningState EnableDdosProtection EnableVmProtection
----------------- ----     -------- ----------------- -------------------- ------------------
RG-Test-Lab       Main-LAN uksouth  Succeeded         False                False

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SO I need to put that information into the Array?

If so How Do I do that (sorry Im at the limit of my PowerShell here)
Pete LongTechnical Consultant

Author

Commented:
So I would need to GET my Virtual Network (already in my script called $azvnetworks )

And feed in

-Name $azvnetworks
-Location $location (already populated)
-AddressPrefix 10.0.0.0/16 (is the same)
-Subnet $azsubnet (already populated)
Most Valuable Expert 2018
Distinguished Expert 2018

Commented:
Assuming the other variables in your first script are already populated, try this:
# $rgName = ...
# $location = ...
# $aznsg = ...
# $pip = ...
$azvnetworks = Get-AzureRmVirtualNetwork -Name 'Main-LAN'
#Create NIC (called MyNicName)
$nicName = "myNicName"
$nic = New-AzureRmNetworkInterface `
	-Name $nicName `
	-ResourceGroupName $rgName `
	-Location $location `
	-SubnetId $azvnetworks.Subnets[0].Id `
	-PublicIpAddressId $pip.Id `
	-NetworkSecurityGroupId $aznsg.Id

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Pete LongTechnical Consultant

Author

Commented:
Hi oBda

$azvnetworks already contains 'Main-LAN"

I'm trying to write this so that it can be used for many different scenarios - having the name of my Virtual Test network in the script will negate that

(background: This script connects the VMware Center locally via PowerCLI - downloads a selected VM converts it from VMDK to VHD then uploads it into Aure and creates a VM) it's the creating the VM part I'm struggling with, everything else works ok, for each piece of information required, it lists all the options and asks you to input the one you want, thats why $aznetworks is already populated, the person running the script picked and entered it)

Would it not be better to do something like

$azvnetworkTEMP = Get-AzureRmVirtualNetwork {where name is equal to $azvnetwork}

Whatever the code would be for that?

Does that make sense?

</P>
Qlemo"Batchelor", Developer and EE Topic Advisor
Top Expert 2015

Commented:
Of course you can do that. You can either use
$azvnetworks = Get-AzureRmVirtualNetwork (Read-Host -Prompt 'Enter Virtual Netwotk NAME (from above);')

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(and not change anything on the other lines) if you do not need the name again, or if you do
$azvnetworks = Read-Host -Prompt 'Enter Virtual Netwotk NAME (from above);'
$azvnetworksTemp = Get-AzureRmVirtualNetwork $azvnetworks

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and then refer to that new var below that lines.
Pete LongTechnical Consultant

Author

Commented:
Hi Qlemo

Thanks for the follow up

If I do that then all the other pieces wont go into the array? will they?

-ResourceGroupName $rgName `
-Location $location `
-SubnetId $azvnetworks.Subnets[0].Id `
-PublicIpAddressId $pip.Id `
-NetworkSecurityGroupId $aznsg.Id

Forgive me Im a firewall engineer script/code is not my thing?

P
Most Valuable Expert 2018
Distinguished Expert 2018
Commented:
PowerShell works with objects with multiple properties and methods.
The $vnet from the MS page is not a string. It's an object representing the virtual network.
The $azvnetworks you get from Read-Host is a plain old string.
Since you already have a Virtual Network, you don't need to create a new one, but you still need the object that represents said network, not just the object's "Name" property as a string variable. The string variable containing 'Main-LAN' "knows" exactly nothing about your Azure infrastructure, so it doesn't have a property "Subnets".
The "Get-AzureRmVirtualNetwork -Name $azvnetworks" will return this object.
The "-ResourceGroupName $rgName ` ..." list is not an array - these are the arguments for New-AzureRmNetworkInterface; the backtick is the line continuation character in PS.
# $rgName = ...
# $location = ...
# $aznsg = ...
# $pip = ...
$azvnetworks = Read-Host -Prompt 'Enter Virtual Netwotk NAME (from above)'
$vnet = Get-AzureRmVirtualNetwork -Name $azvnetworks
#Create NIC (called MyNicName)
$nicName = "myNicName"
$nic = New-AzureRmNetworkInterface `
	-Name $nicName `
	-ResourceGroupName $rgName `
	-Location $location `
	-SubnetId $vnet.Subnets[0].Id `
	-PublicIpAddressId $pip.Id `
	-NetworkSecurityGroupId $aznsg.Id

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Pete LongTechnical Consultant

Author

Commented:
Thanks for putting me straight :)

$vnet = Get-AzureRmVirtualNetwork -Name $azvnetworks

Threw an error, it needs the ResourceGroupName as well

$vnet = Get-AzureRmVirtualNetwork -Name $azvnetworks -ResourceGroupName $aznsg

Thanks again

P

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