class ActiveRecord::Relation::FromClause

def self.empty
  @empty ||= new(nil, nil).freeze
end

def ==(other)
  self.class == other.class && value == other.value && name == other.name
end

def empty?
  value.nil?
end

def initialize(value, name)
  @value = value
  @name = name
end

def merge(other)
  self
end