Metadata keys allow any non-empty string.

[pithos-macos] / pithos-apple-common

diff --git a/pithos-apple-common b/pithos-apple-common
index 25cafff..6d3af6e 160000 (submodule)
--- a/pithos-apple-common
+++ b/pithos-apple-common
@@ -1 +1 @@
-Subproject commit 25cafffeaeaa994a761f9bacd5efc80308f3f60c
+Subproject commit 6d3af6ef2539e07a14f3d860c4bb1ec063f9fe8a