[Flow] Content security does'nt work

[Falk]

The content security works so far but now I've the problem that I did'nt find a possibility to negate the following expression:

entities:
  'My\Package\Domain\Model\Contractor':
     My_Package_Contractors_Related: 'this.users contains current.securityContext.party'

The contractors are associated with the users but with this expression I get only this contractors without realtion to users. How can I negate 'this.users contains current.securityContext.party'?

I've tried the following but nothing worked for me:
'this.users ! contains current.securityContext.party'
'this.users != NULL &&! this.users contains current.securityContext.party'
'TRUE == TRUE &&! this.users contains current.securityContext.party'

Thanks Falk