add nil#to_h; ref #2348

mrbgems/mruby-enum-ext/mrblib/enum.rb

@@ -691,4 +691,8 @@ module Enumerable
     end
     h
   end
+
+  def nil.to_h
+    {}
+  end
 end

mrbgems/mruby-enum-ext/test/enum.rb

@@ -157,4 +157,6 @@ assert("Enumerable#to_h") do
   h = c.new.to_h
   assert_equal Hash, h.class
   assert_equal h0, h
+  # mruby-enum-ext also provides nil.to_h
+  assert_equal Hash.new, nil.to_h
 end