The issue

/libraries/legacy/view/legacy.php
inside comments (line 342) of function assignRef

   * <code>
   * $view = new JView;
   *
   * // Assign by name and value
   * $view->assignRef('var1', $ref);
   *
   * // Assign directly
   * $view->ref = &$var1;
   * </code>

Should be:

   * <code>
 * $view = new JView;
 *
 * // Assign by name and value
 * $view->assignRef('var1', $ref);
 *
 * // Assign directly
 * $view->var1 = &$ref;
 * </code>

Reason:

Inside the code, it is:

public function assignRef($key, &$val)
{ //...
		$this->$key = &$val;
 // ... 
}

Joomla core 3.7.0

for instance, a code snipped:

 		//deprecated: $this->assignRef('lists', $this->_lists); //changed to next line:
	$this->lists = &$this->_lists;