Align doc chunks return with EEP 48

lib/elixir/lib/behaviour.ex

@@ -111,9 +111,9 @@ defmodule Behaviour do
         end
       end
 
-      defp __behaviour__doc_value(:none), do: nil
-      defp __behaviour__doc_value(:hidden), do: false
       defp __behaviour__doc_value(%{"en" => doc}), do: doc
+      defp __behaviour__doc_value(:hidden), do: false
+      defp __behaviour__doc_value(_), do: nil
 
       import unquote(__MODULE__)
     end

lib/elixir/lib/code.ex

@@ -1348,7 +1348,7 @@ defmodule Code do
           | {:error, :module_not_found | :chunk_not_found | {:invalid_chunk, binary}}
         when annotation: :erl_anno.anno(),
              beam_language: :elixir | :erlang | atom(),
-             doc_content: %{required(binary) => binary} | :none | :hidden,
+             doc_content: %{optional(binary) => binary} | :none | :hidden,
              doc_element:
                {{kind :: atom, function_name :: atom, arity}, annotation, signature, doc_content,
                 metadata},

lib/elixir/lib/kernel/typespec.ex

@@ -23,6 +23,7 @@ defmodule Kernel.Typespec do
         for {{:type, name, arity}, _, _, doc, _} <- docs do
           case doc do
             %{"en" => doc_string} -> {{name, arity}, doc_string}
+            %{} -> {{name, arity}, nil}
             :none -> {{name, arity}, nil}
             # Hidden or unknown format are ignored
             _ -> {{name, arity}, false}