MDL-61407 question: Add null_writer for all behaviours

Behaviours do not store any personal data.
Any contrib behaviour which does store personal data should utilise the
standard export interfaces as this subsystem will not call them directly.

question/behaviour/interactivecountback/classes/privacy/provider.php

@@ -0,0 +1,46 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Privacy Subsystem implementation for qbehaviour_interactivecountback.
+ *
+ * @package    qbehaviour_interactivecountback
+ * @copyright  2018 Andrew Nicols <[email protected]>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+namespace qbehaviour_interactivecountback\privacy;
+
+defined('MOODLE_INTERNAL') || die();
+
+/**
+ * Privacy Subsystem for qbehaviour_interactivecountback implementing null_provider.
+ *
+ * @copyright  2018 Andrew Nicols <[email protected]>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class provider implements \core_privacy\local\metadata\null_provider {
+
+    /**
+     * Get the language string identifier with the component's language
+     * file to explain why this plugin stores no data.
+     *
+     * @return  string
+     */
+    public static function get_reason() : string {
+        return 'privacy:metadata';
+    }
+}

question/behaviour/interactivecountback/lang/en/qbehaviour_interactivecountback.php

@@ -24,3 +24,4 @@
  */
 
 $string['pluginname'] = 'Interactive with multiple tries (credit for earlier tries)';
+$string['privacy:metadata'] = 'The Interactive with multiple tries (credit for earlier tries) question behaviour plugin does not store any personal data.';