Fixes failed tests for Data Object

- fixed currency renderer for grid columns

Author: andrewbess

app/code/Magento/Backend/Block/Widget/Grid/Column/Renderer/Currency.php

@@ -102,7 +102,9 @@ protected function _getCurrencyCode($row)
         if ($code = $this->getColumn()->getCurrencyCode()) {
             return $code;
         }
-        if ($code = $row->getData($this->getColumn()->getCurrency())) {
+        $currency = $this->getColumn()->getCurrency();
+
+        if ($currency !== null && $code = $row->getData($currency)) {
             return $code;
         }