print nothing

[aminya]

For Julia <= 1.2 the following method is not defined.

if VERSION <=  v"1.2"
    Base.print(io, ::Nothing) = Base.print(io, "")
    Base.print(::Base.GenericIOBuffer{Array{UInt8,1}}, ::Nothing) = Base.print(io, "")
    Base.string(::Nothing) = ""
end