Option write_empty_value

Specifies the object that is to be substituted for each field that has an empty String.

Default value:

CSV::DEFAULT_OPTIONS.fetch(:write_empty_value) # => ""

Without the option:

str = CSV.generate_line(['a', '', 'c', ''])
str # => "a,\"\",c,\"\"\n"

With the option:

str = CSV.generate_line(['a', '', 'c', ''], write_empty_value: "x")
str # => "a,x,c,x\n"