Check null for acl-fields

tests/src/Util/ACLFormaterTest.php

@@ -2,6 +2,7 @@
 
 namespace Friendica\Test\src\Util;
 
+use Error;
 use Friendica\Model\Group;
 use Friendica\Util\ACLFormatter;
 use PHPUnit\Framework\TestCase;
@@ -162,6 +163,18 @@ class ACLFormaterTest extends TestCase
 		$this->assertEquals(array('1', '3'), $aclFormatter->expand($text));
 	}
 
+	/**
+	 * Test expected exception in case of wrong typehint
+	 *
+	 * @expectedException Error
+	 */
+	public function testExpandNull()
+	{
+		$aclFormatter = new ACLFormatter();
+
+		$aclFormatter->expand(null);
+	}
+
 	public function dataAclToString()
 	{
 		return [