add support for PHP8 (#114)

.travis.yml

@@ -4,10 +4,12 @@ services:
   # wp-publications is a Wordpress plugin, wordpress requires mysql
   - mysql
 
+# doc at https://docs.travis-ci.com/user/languages/php/
 php:
   - '7.2' # release 30 November 2017
   - '7.3' # release 6 December 2018
   - '7.4' # release 28 November 2019
+  - '8.0'
 
 script:
     - curl -L -o reflectivedoc.php https://www.monperrus.net/martin/reflectivedoc.php.txt

bibtexbrowser.php

@@ -3123,7 +3123,7 @@ class SimpleDisplay  {
 
   var $headingLevel = BIBTEXBROWSER_HTMLHEADINGLEVEL;
 
-  function __construct($db = NULL, $query = NULL) {
+  function __construct($db = NULL, $query = array()) {
     if ($db == NULL) return;
     $this->setEntries($db->multisearch($query));
   }