The administration and maintenance of Microsoft Exchange Server to ensure secure, reliable, and efficient email and collaboration services across an organization.
You need to remove the quotes around $null, otherwise it will take it as a string value (i.e. it will only match users for which Title is set to the "$null" string value). Here's a working example:
Set-DynamicDistributionGroup test -RecipientFilter {(Office -like "Home") -and ((-not(RecipientTypeDetailsvalue -eq 'RoomMailbox')) -and (-not(RecipientTypeDetailsvalue -eq 'SharedMailbox')) -and (-not(RecipientType -eq 'MailContact')) -and (Title -ne $null))}