Test for error value from apply_recipe fallback. (#95)

RecipesPipeline/src/plot_recipe.jl

@@ -31,15 +31,20 @@ function _process_plotrecipe(plt, kw, kw_list, still_to_process)
         st = kw[:seriestype]
         st = kw[:seriestype] = type_alias(plt, st)
         datalist = RecipesBase.apply_recipe(kw, Val{st}, plt)
-        warn_on_recipe_aliases!(plt, datalist, :plot, st)
-        for data in datalist
-            preprocess_attributes!(plt, data.plotattributes)
-            if data.plotattributes[:seriestype] == st
-                error("Plot recipe $st returned the same seriestype: $(data.plotattributes)")
+        if !isnothing(datalist)
+            warn_on_recipe_aliases!(plt, datalist, :plot, st)
+            for data in datalist
+                preprocess_attributes!(plt, data.plotattributes)
+                if data.plotattributes[:seriestype] == st
+                    error("Plot recipe $st returned the same seriestype: $(data.plotattributes)")
+                end
+                push!(still_to_process, data.plotattributes)
             end
-            push!(still_to_process, data.plotattributes)
+        else
+            push!(kw_list, kw)
         end
     catch err
+        # the try/catch block can be removed when Plots.jl makes the compensating change
         if err isa MethodError && occursin("plot recipe", err.args)
             push!(kw_list, kw)
         else