参考：https://www.codecademy.com/en/forum_questions/50fe886f68fc44056f00626c
require 'bigdecimal'
require 'bigdecimal/util'
0.28.to_d * 100
nil.to_d => 0.0
''.to_d => 0.0
"abc".to_d => 0.0
Ruby 使用bigdecimal处理大数据
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