Further changes to fix unit tests and keep things backwards compatible.

I'm really not happy with how Magento is using the magic __call method and I would propose to deprecated the behavior.

Author: igorwulff

lib/internal/Magento/Framework/DataObject.php

@@ -389,23 +389,17 @@ public function __call($method, $args)
     {
         switch ($method[0].($method[1] ?? '').($method[2] ?? '')) {
             case 'get':
-                if (isset($args[0]) && $args[0] !== null) {
-                    return $this->getData(
-                        self::$_underscoreCache[$method] ?? $this->_underscore($method),
-                        $args[0]
-                    );
-                }
-
                 return $this->_data[
                     self::$_underscoreCache[$method] ?? $this->_underscore($method)
                 ] ?? $this->getData(
-                    self::$_underscoreCache[$method] ?? $this->_underscore($method)
+                    self::$_underscoreCache[$method] ?? $this->_underscore($method),
+                        $args[0] ?? null
                 );
             case 'set':
-                $this->_data[
-                    self::$_underscoreCache[$method] ?? $this->_underscore($method)
-                ] = $args[0] ?? null;
-                return $this;
+                return $this->setData(
+                    self::$_underscoreCache[$method] ?? $this->_underscore($method),
+                    $args[0] ?? null
+                );
             case 'uns':
                 return $this->unsetData(
                     self::$_underscoreCache[$method] ?? $this->_underscore($method)