The "New-NcVol" cmdlet will accept a null value for the JunctionPath parameter if you don't need/want a junction path specified during volume creation.
PS H:\> New-NcVol -VserverContext lab-svm01 -Name volume001 -Aggregate aggr1_ssd_n1 -size 1GB -JunctionPath $null
Name State TotalSize Used Available Dedupe Aggregate Vserver
---- ----- --------- ---- --------- ------ --------- -------
volume001 online 1.0 GB 0% 972.6 MB False aggr1_ssd_n1 lab-svm01
PS H:\> Get-NcVol volume001 | fl JunctionPath
JunctionPath :