gistfile1.rb

#!/usr/bin/env ruby
# coding: utf-8

require "csv"

rows = [
  [nil, "ほげ"],
  ["", "ほげ"]
]

puts CSV.generate("", force_quotes:true){|csv|
  rows.map{|row| csv << row}
}

puts CSV.generate(""){|csv|
  rows.map{|row| csv << row}
}

puts CSV.generate("", col_sep:"\t"){|csv|
  rows.map{|row| csv << row}
}