Looking at the mentioned question, it seems a NULL pointer arrives as first argument in phutil_encode_log(). Fortunately that function is used by only 3 places:

• arcanist PhutilJSONProtocolChannel.php phutil_encode_log($len): no problem, the arg is a string
• arcanist PhutilJSONProtocolChannel.php phutil_encode_log(substr(...)): as above
• arcanist PhutilDeferredLog.php phutil_encode_log($map[$c]): 🔶 maybe here it arrives a null pointer instead of a string

But, without a stack trace, we will not find consensus to proceed. Also, I'm unsure if the solution is something like this:

diff --git a/src/filesystem/PhutilDeferredLog.php b/src/filesystem/PhutilDeferredLog.php
index 2193eb3c..fc758439 100644
--- a/src/filesystem/PhutilDeferredLog.php
+++ b/src/filesystem/PhutilDeferredLog.php
@@ -229,7 +229,7 @@ final class PhutilDeferredLog extends Phobject {
       if ($saw_percent) {
         $saw_percent = false;
         if (array_key_exists($c, $map)) {
-          $result .= phutil_encode_log($map[$c]);
+          $result .= phutil_encode_log(coalesce($map[$c], ''));
         } else {
           $result .= '-';
         }

Since there is a possibility that the root problem is under one consumer like PhutilDeferredLog#setData( array( 'something' => NULL ) ) somewhere.

If you can, please share a stack trace. Thanks my friend.