code: public void dropUser(String name) {
  
          boolean reservedUser = GranteeManager.isReserved(name);
  
          if (reservedUser) {
              throw Error.error(ErrorCode.X_28502, name);
          }
  
          boolean result = granteeManager.removeGrantee(name);
  
          if (!result) {
              throw Error.error(ErrorCode.X_28501, name);
          }
  
          User user = (User) userList.remove(name);
  
          if (user == null) {
              throw Error.error(ErrorCode.X_28501, name);
          }
      }
docs: Attempts to drop a User object with the specified name
  from this object's set. <p>
  
  A successful drop action consists of: <p>
  
  <UL>
  
  <LI>removing the User object with the specified name
  from the set.
  
  <LI>revoking all rights from the removed User<br>
  (this ensures that in case there are still references to the
  just dropped User object, those references
  cannot be used to erronously access database objects).
  
  </UL> <p>