Make IDNA return an empty string when the input is empty. Fixes #1163178.
Will backport to 2.4.
diff --git a/Misc/NEWS b/Misc/NEWS
index 20e1f89..89efcad 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -193,6 +193,8 @@
 Library
 -------
 
+- Bug #1163178: Make IDNA return an empty string when the input is empty.
+
 - Patch #848017: Make Cookie more RFC-compliant. Use CRLF as default output
   separator and do not output trailing semicola.