GETWO-1556] Export: Unable to Filter Data by Attribute With Input Typ…

…e Multiple Select

    Changed variable scope to be private

app/code/Magento/ImportExport/Model/Export.php

@@ -70,7 +70,7 @@ class Export extends \Magento\ImportExport\Model\AbstractModel
     /**
      * @var array
      */
-    protected static $backendTypeToFilterMapper = [
+    private static $backendTypeToFilterMapper = [
         'datetime' => self::FILTER_TYPE_DATE,
         'decimal' => self::FILTER_TYPE_NUMBER,
         'int' => self::FILTER_TYPE_NUMBER,