Problem trying to add UNDP to node

So in the interest of keeping things simple, this is what I'm sending in Powershell:

$result = New-SwisObject $swis –EntityType 'Orion.NPM.CustomPollerAssignmentOnNode' -Properties @{CustomPollerID='0a5ddec7-57b0-45a2-a595-37311bf5d88c';NodeID='10101';}

This is the result I'm getting back:

New-SwisObject : Cannot insert the value NULL into column 'AssignmentName', table 'CPMIT.dbo.CustomPollerAssignment'; column does not allow nulls. INSERT fails.

Running core  2018.2 HF6

Any ideas?