diff --git a/src/mod_http_api.erl b/src/mod_http_api.erl
index 881587ede..a189777b1 100644
--- a/src/mod_http_api.erl
+++ b/src/mod_http_api.erl
@@ -273,7 +273,7 @@ handle(Call, Auth, Args, Version) when is_atom(Call), is_list(Args) ->
                     fun ({Key, binary}, Acc) ->
                             [{Key, <<>>}|Acc];
                         ({Key, string}, Acc) ->
-                            [{Key, <<>>}|Acc];
+			    [{Key, ""}|Acc];
                         ({Key, integer}, Acc) ->
                             [{Key, 0}|Acc];
                         ({Key, {list, _}}, Acc) ->
@@ -406,10 +406,10 @@ format_arg(Elements, {list, ElementsDef})
 format_arg(Arg, integer) when is_integer(Arg) -> Arg;
 format_arg(Arg, binary) when is_list(Arg) -> process_unicode_codepoints(Arg);
 format_arg(Arg, binary) when is_binary(Arg) -> Arg;
-format_arg(Arg, string) when is_list(Arg) -> process_unicode_codepoints(Arg);
-format_arg(Arg, string) when is_binary(Arg) -> Arg;
+format_arg(Arg, string) when is_list(Arg) -> Arg;
+format_arg(Arg, string) when is_binary(Arg) -> binary_to_list(Arg);
 format_arg(undefined, binary) -> <<>>;
-format_arg(undefined, string) -> <<>>;
+format_arg(undefined, string) -> "";
 format_arg(Arg, Format) ->
     ?ERROR_MSG("don't know how to format Arg ~p for format ~p", [Arg, Format]),
     throw({invalid_parameter,