Raise error if channel_{id,secret} is not configured

Author: mizoR

lib/line/bot/client.rb

@@ -63,6 +63,9 @@ def credentials
       #
       # @return [Net::HTTPResponse]
       def issue_channel_token(grant_type = 'client_credentials')
+        channel_id_required
+        channel_secret_required
+
         payload = URI.encode_www_form(
           grant_type:    grant_type,
           client_id:     channel_id,
@@ -616,6 +619,14 @@ def secure_compare(a, b)
       def channel_token_required
         raise ArgumentError, '`channel_token` is not configured' unless channel_token
       end
+
+      def channel_id_required
+        raise ArgumentError, '`channel_id` is not configured' unless channel_id
+      end
+
+      def channel_secret_required
+        raise ArgumentError, '`channel_secret` is not configured' unless channel_secret
+      end
     end
   end
 end