title: Odoo v11, Error: "res.users, Operation: read None", while creating a new user and assign to new company
body: <p>I have a problem creating a new user on Odoo and assign to a company that I created v. 11.</p>
  
  <p>First on companies I created a new company name "XXXX".</p>
  
  <p>Then I created a new user "YYY" and on the multicompany field I assigned on "allowed companies" the company "XXXX", and on "Current Company" I assigned the company "XXXX".
  The problem is that when i try to save the new user created I received this error:</p>
  
  <p>"Error while validating constraint</p>
  
  <p>The requested operation cannot be completed due to security restrictions. Please contact your system administrator.</p>
  
  <p>(Document type: res.users, Operation: read)
  None "</p>
  
  <p>The only way i can save the new user is by selecting on the field "Allowed Companies" the default company created from the system.</p>
  
  <p>Is there something I did wrong while creating the new company "XXXX" or is there some relation and/or rights that are particular important between user and company?</p>