I’m sure it’s not URE Pro bug. Your notification is the 1st for the perion this part of code stays unchanged.
Let’s trace the code from line #222, which causes the PHP fatal error:
user-role-editor.php: #37: define( 'URE_PLUGIN_FULL_PATH', __FILE__ );
pro/includes/classes/user-role-editor-pro.php: #54: $ure_update_checker = new PluginUpdateChecker(URE_UPDATE_URL . '?action=get_metadata&slug=user-role-editor-pro', URE_PLUGIN_FULL_PATH);
pro/includes/plugin-update-checker.php: #52: $this->pluginAbsolutePath = $pluginFile;
pro/includes/plugin-update-checker.php: #53: $this->pluginFile = plugin_basename($this->pluginAbsolutePath);
pro/includes/plugin-update-checker.php: #222: $pluginInfo->filename = $this->pluginFile;
As you can see from the code above $this->pluginFile at the line 222 can not be null, if exactly this code is executed. It just processes PHP built-in __FILE__ constant value.
I suppose that you may use another plugin, which also use PluginUpdateChecker class, but defined earlier due to code execution queue and possibly another version, which may lead to a conflict. Check your plugins source code using command similar
grep -rn ‘PluginUpdateChecker’