Default timezone check

src/Plugin/views/sort/FuturePastDate.php

@@ -75,8 +75,13 @@ class FuturePastDate extends Date {
     // .
     $this->ensureMyTable();
 
-    // Calculate the user's timezone offset.
-    $timezone = new \DateTimeZone($this->account->getTimeZone());
+    // Calculate the user's timezone offset. Default to UTC.
+    if($this->account->getTimeZone()) {
+      $timezone = new \DateTimeZone($this->account->getTimeZone());
+    } else {
+      $timezone = new \DateTimeZone('UTC');
+    }
+
     $offset = $timezone->getOffset(new \DateTime());
 
     $date_alias = "UNIX_TIMESTAMP($this->tableAlias.$this->realField) - $offset";