Add `passage_span_context_null` module
diff --git a/src/passage_span_context.erl b/src/passage_span_context.erl
index 1346aa4..62ffc2a 100644
--- a/src/passage_span_context.erl
+++ b/src/passage_span_context.erl
@@ -26,11 +26,11 @@
%%------------------------------------------------------------------------------
%% Callback API
%%------------------------------------------------------------------------------
--callback make_span_context(passage_span:normalized_refs()) -> context().
+-callback make_span_context_state(passage_span:normalized_refs()) -> state().
--callback inject_span_context(context(), format(), carrier(), inject_fun()) -> carrier().
+-callback inject_span_context(context(), format(), inject_fun(), carrier()) -> carrier().
--callback extract_span_context(format(), carrier(), iterate_fun()) -> {ok, context()} | error.
+-callback extract_span_context(format(), iterate_fun(), carrier()) -> {ok, context()} | error.
%%------------------------------------------------------------------------------
%% Macros & Records
diff --git a/src/passage_span_context_null.erl b/src/passage_span_context_null.erl
new file mode 100644
index 0000000..132407b
--- /dev/null
+++ b/src/passage_span_context_null.erl
@@ -0,0 +1,27 @@
+%% @copyright 2017 Takeru Ohta <phjgt308@gmail.com>
+%%
+%% @doc TODO
+%%
+-module(passage_span_context_null).
+
+-behaviour(passage_span_context).
+
+%%------------------------------------------------------------------------------
+%% 'passage_span_context' Callback API
+%%------------------------------------------------------------------------------
+-export([make_span_context_state/1, inject_span_context/4, extract_span_context/3]).
+
+%%------------------------------------------------------------------------------
+%% 'passage_span_context' Callback Functions
+%%------------------------------------------------------------------------------
+%% @private
+make_span_context_state(_Refs) ->
+ undefined.
+
+%% @private
+inject_span_context(_Context, _Format, _InjectFun, Carrier) ->
+ Carrier.
+
+%% @private
+extract_span_context(_Format, _IterateFun, _Carrier) ->
+ error.
