diff --git a/src/filesystem/Filesystem.php b/src/filesystem/Filesystem.php
--- a/src/filesystem/Filesystem.php
+++ b/src/filesystem/Filesystem.php
@@ -275,7 +275,7 @@
       $trap->destroy();
 
       if (!$ok) {
-        if (strlen($err)) {
+        if ($err !== null && strlen($err)) {
           throw new FilesystemException(
             $to,
             pht(
@@ -307,7 +307,7 @@
    * @task   file
    */
   public static function remove($path) {
-    if (!strlen($path)) {
+    if ($path == null || !strlen($path)) {
       // Avoid removing PWD.
       throw new Exception(
         pht(
@@ -673,7 +673,7 @@
     }
 
     // If we come back with an encoding, strip it off.
-    if (strpos($mime_type, ';') !== false) {
+    if ($mime_type !== null && strpos($mime_type, ';') !== false) {
       list($type, $encoding) = explode(';', $mime_type, 2);
       $mime_type = $type;
     }
diff --git a/src/workingcopyidentity/ArcanistWorkingCopyIdentity.php b/src/workingcopyidentity/ArcanistWorkingCopyIdentity.php
--- a/src/workingcopyidentity/ArcanistWorkingCopyIdentity.php
+++ b/src/workingcopyidentity/ArcanistWorkingCopyIdentity.php
@@ -289,7 +289,7 @@
   }
 
   public function readLocalArcConfig() {
-    if (strlen($this->localMetaDir)) {
+    if ($this->localMetaDir !== null && strlen($this->localMetaDir)) {
       $local_path = Filesystem::resolvePath('arc/config', $this->localMetaDir);
 
       $console = PhutilConsole::getConsole();