diff --git a/core/Plugin/Report.php b/core/Plugin/Report.php
index b2a42317db6984f0791d0e20a831313e21ef8358..b09fed2d9a06be7ec799dda243ba58ec51054a37 100644
--- a/core/Plugin/Report.php
+++ b/core/Plugin/Report.php
@@ -32,7 +32,7 @@ class Report
     protected $widgetTitle;
     protected $widgetParams = array();
     protected $menuTitle;
-    protected $processedMetrics = null;
+    protected $processedMetrics = array();
     protected $hasGoalMetrics = false;
     protected $metrics = array();
     protected $constantRowsCount = null;