Optimize RDF.PrefixMap.new/1 creation from another PrefixMap

lib/rdf/prefix_map.ex

@@ -23,6 +23,8 @@ defmodule RDF.PrefixMap do
   """
   def new(map)
 
+  def new(%__MODULE__{} = prefix_map), do: prefix_map
+
   def new(map) when is_map(map) do
     %__MODULE__{map: Map.new(map, &normalize/1)}
   end

test/unit/prefix_map_test.exs

@@ -45,6 +45,10 @@ defmodule RDF.PrefixMapTest do
              ) == @example2
     end
 
+    test "with another prefix map" do
+      assert PrefixMap.new(@example2) == @example2
+    end
+
     test "when the IRI namespace is given as a RDF.Vocabulary.Namespace" do
       assert PrefixMap.new(
                ex1: "http://example.com/foo/",