preserving nulls in int vectors

[thoughtafter]

I noticed this inconsistent behavior:

[1] pry(main)> require 'rserve'
=> true
[2] pry(main)> Rserve::REXP::Integer.new([nil, nil]).to_ruby
=> [0, 0]
[3] pry(main)> Rserve::REXP::Double.new([nil, nil]).to_ruby
=> [nil, nil]

It seems int vectors lose nulls and double vectors keep them. This is due to:
https://github.com/clbustos/Rserve-Ruby-client/blob/master/lib/rserve/rexp/integer.rb#L14

 data.map {|v| v.to_i}

Since nil.to_i == 0 this will wipe out nulls.

[thoughtafter]

So I thought I have fixed this in code that I'm using and found it's trickier than I had first guessed.

require 'rserve'
con=Rserve::Connection.new
con.assign("v", Rserve::REXP::Integer.new([1, 2, nil, nil])).to_ruby
con.eval("v").to_ruby

The nil's are replaced with zeros. However, if
data.map {|v| v.to_i} is changed to say:
data.map {|v| v.try(:to_int)} the nils are preserved in the Rserve::REXP::Integer.new but the assignment will fail due to calling Protocol.set_int with a non-integer.