Smarty v5 update test, initial code setup

src/Compile/Modifier/DefaultModifierCompiler.php

@@ -0,0 +1,26 @@
+<?php
+namespace Smarty\Compile\Modifier;
+/**
+ * Smarty default modifier plugin
+ * Type:     modifier
+ * Name:     default
+ * Purpose:  designate default value for empty variables
+ *
+ * @author Uwe Tews
+ */
+
+class DefaultModifierCompiler extends Base {
+
+	public function compile($params, \Smarty\Compiler\Template $compiler) {
+		$output = $params[ 0 ];
+		if (!isset($params[ 1 ])) {
+			$params[ 1 ] = "''";
+		}
+		array_shift($params);
+		foreach ($params as $param) {
+			$output = '(($tmp = ' . $output . ' ?? null)===null||$tmp===\'\' ? ' . $param . ' ?? null : $tmp)';
+		}
+		return $output;
+	}
+
+}