MethodError in concrete rectification plot

[mforets]

If we use the definition in #2643, then:

using Random

Random.seed!(11)

P = rand(HPolygon)
R = rectify(P)

plot(P)
plot!(R, 1e-2)

MethodError: no method matching low(::∅)
Closest candidates are:
  low(::AbstractSingleton) at /home/mforets/.julia/dev/LazySets/src/Interfaces/AbstractSingleton.jl:120
  low(::AbstractSingleton, ::Int64) at /home/mforets/.julia/dev/LazySets/src/Interfaces/AbstractSingleton.jl:139
  low(::Interval{N, IN} where IN<:IntervalArithmetic.AbstractInterval{N}) where N at /home/mforets/.julia/dev/LazySets/src/Sets/Interval.jl:298
  ...

Stacktrace:
  [1] _update_plot_limits!(lims::Dict{Any, Any}, X::LinearMap{Float64, Intersection{Float64, HPolygon{Float64, Vector{Float64}}, HPolyhedron{Float64, LazySets.Arrays.SingleEntryVector{Float64}}}, Float64, Diagonal{Float64, Vector{Float64}}})
    @ LazySets ~/.julia/dev/LazySets/src/Plotting/plot_recipes.jl:48
  [2] macro expansion
    @ ~/.julia/dev/LazySets/src/Plotting/plot_recipes.jl:321 [inlined]
  [3] apply_recipe(plotattributes::AbstractDict{Symbol, Any}, X::LinearMap{Float64, Intersection{Float64, HPolygon{Float64, Vector{Float64}}, HPolyhedron{Float64, LazySets.Arrays.SingleEntryVector{Float64}}}, Float64, Diagonal{Float64, Vector{Float64}}}, ε::Float64)
    @ LazySets ~/.julia/packages/RecipesBase/92zOw/src/RecipesBase.jl:282
  [4] _process_userrecipes!(plt::Any, plotattributes::Any, args::Any)
    @ RecipesPipeline ~/.julia/packages/RecipesPipeline/CirY4/src/user_recipe.jl:36
  [5] recipe_pipeline!(plt::Any, plotattributes::Any, args::Any)
    @ RecipesPipeline ~/.julia/packages/RecipesPipeline/CirY4/src/RecipesPipeline.jl:70
  [6] _plot!(plt::Plots.Plot, plotattributes::Any, args::Any)
    @ Plots ~/.julia/packages/Plots/SVksJ/src/plot.jl:172
  [7] plot!(::Plots.Plot, ::Any, ::Vararg{Any, N} where N; kw::Any)
    @ Plots ~/.julia/packages/Plots/SVksJ/src/plot.jl:162
  [8] plot!(::Plots.Plot, ::Any, ::Vararg{Any, N} where N)
    @ Plots ~/.julia/packages/Plots/SVksJ/src/plot.jl:159
  [9] plot!(::Any, ::Vararg{Any, N} where N; kw::Any)
    @ Plots ~/.julia/packages/Plots/SVksJ/src/plot.jl:153
 [10] plot!(::Any, ::Any)
    @ Plots ~/.julia/packages/Plots/SVksJ/src/plot.jl:147
 [11] top-level scope
    @ In[57]:9
 [12] eval
    @ ./boot.jl:360 [inlined]
 [13] include_string(mapexpr::typeof(REPL.softscope), mod::Module, code::String, filename::String)
    @ Base ./loading.jl:1094

[mforets]

This can be solved by adding an emptiness check: isempty(box) && return nothing,