Default for `:info` ?

When testing RLInterface on `POMDPs#version-0.8` I am getting the following error:
` KeyError: key :info not found`
which results from a call to:
```julia
s, r, info = gen(DDNOut(:sp, :r, :info), env.problem, env.state, a, env.rng)
```

I realized there is no default for :info anymore: https://github.com/JuliaPOMDP/POMDPModelTools.jl/blob/master/src/info.jl#L84

- Do we want a default that outputs `nothing` ?
- If yes, what is the proper way to implement it?
e.g. `POMDPs.gen(out::DDNOut{(:sp,:o,:r,:info)}, m, s, a, rng) = (gen(out, m, s, a, rng)..., nothing)` , but with a smarter way to handle all the combination for `out`
- If not, what is the proper way to check if `:info` is available?