code: public void revokeAllPermissions(Grantee grantee) {
          ArrayList<Grant> grantsToRemove = new ArrayList<Grant>();
          List<Grant> existingGrants = getGrantsAsList();
          for (Grant gap : existingGrants) {
              if (gap.getGrantee().equals(grantee)) {
                  grantsToRemove.add(gap);
              }
          }
          grantList.removeAll(grantsToRemove);
      }
docs: Revokes the permissions of a grantee by removing the grantee from the access control list (ACL).
  
  @param grantee
  The grantee to remove from this ACL.