Replace Nullable{T} with Union{T, Nothing}

src/components.jl

@@ -443,7 +443,7 @@ mutable struct SeriesAnnotations
 end
 function series_annotations(strs::AbstractVector, args...)
     fnt = font()
-    shp = Nullable{Any}()
+    shp = Union{Any, Nothing}()
     scalefactor = (1,1)
     for arg in args
         if isa(arg, Shape) || (isa(arg, AbstractVector) && eltype(arg) == Shape)

src/plot.jl

@@ -1,8 +1,8 @@
 
 mutable struct CurrentPlot
-    nullableplot::Nullable{AbstractPlot}
+    nullableplot::Union{AbstractPlot, Nothing}
 end
-const CURRENT_PLOT = CurrentPlot(Nullable{AbstractPlot}())
+const CURRENT_PLOT = CurrentPlot(Union{AbstractPlot, Nothing}())
 
 isplotnull() = isnull(CURRENT_PLOT.nullableplot)