另一种解决方案是使用Refinements，如下所示:

module Nothingness
  refine Numeric do
    alias_method :nothing?, :zero?
  end

  refine NilClass do
    alias_method :nothing?, :nil?
  end
end

using Nothingness

if discount.nothing?
  # do something
end

if discount.nil? || discount == 0
  [do something]
end

if (discount||0) != 0
  #...
end

unless [nil, 0].include?(discount) 
  # ...
end

在处理数据库记录时，我喜欢使用迁移帮助器将所有空值初始化为0:

add_column :products, :price, :integer, default: 0

if discount and discount != 0
  ..
end

更新，它将为false折扣= false