diff --git a/src/applications/multimeter/controller/MultimeterSampleController.php b/src/applications/multimeter/controller/MultimeterSampleController.php
--- a/src/applications/multimeter/controller/MultimeterSampleController.php
+++ b/src/applications/multimeter/controller/MultimeterSampleController.php
@@ -10,7 +10,10 @@
     $viewer = $this->getViewer();
     $group_map = $this->getColumnMap();
 
-    $group = explode('.', $request->getStr('group'));
+    $group = [];
+    if (phutil_nonempty_string($request->getStr('group'))) {
+      $group = explode('.', $request->getStr('group'));
+    }
     $group = array_intersect($group, array_keys($group_map));
     $group = array_fuse($group);