Foreach statement to copy unified group members

Looking for help in getting input from a .csv file for copying group members from one group to another.  Both are Unified groups.

This code works for a single group to group copy:

$List = Get-UnifiedGroupLinks -Identity "Group1" -LinkType Members | Select-Object -expandproperty name
Add-UnifiedGroupLinks -Identity "Group2" -LinkType Members -Links $List

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This is what I setup in for foreach:

$Groups = Import-Csv -Path .\GroupInput.csv
foreach ($Group in $Groups) {
    $List = Get-UnifiedGroupLinks -Identity $_.SourceGroup -LinkType Members | Select-Object -expandproperty name
    Add-UnifiedGroupLinks -Identity $_.TargetGroup -LinkType Members -Links $List
}

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Error I'm getting is:
Cannot bind argument to parameter 'Identity' because it is null.
    + CategoryInfo          : InvalidData: (:) [Get-UnifiedGroupLinks], ParameterBindingValidationException
    + FullyQualifiedErrorId : ParameterArgumentValidationErrorNullNotAllowed,Get-UnifiedGroupLinks
    + PSComputerName        : outlook.office365.com

GroupInput.csv:
SourceGroup,TargetGroup
Group1,Group2