code: func (s *propOuterJoinConstSolver) pickNewEQConds(visited []bool) map[int]*Constant {
  	retMapper := make(map[int]*Constant)
  	retMapper = s.pickEQCondsOnOuterCol(retMapper, visited, true)
  	if retMapper == nil {
  		// Filter is constant false or error occurred, enforce early termination.
  		return nil
  	}
  	retMapper = s.pickEQCondsOnOuterCol(retMapper, visited, false)
  	return retMapper
  }
docs: // pickNewEQConds picks constant equal expressions from join and filter conditions.