Error in hook_openid_connect_userinfo_alter() if $userinfo is NULL

Problem/Motivation

The following error occurs when the retrieval of user information fails and $userinfo becomes NULL.

TypeError: Argument 1 passed to mymodule_openid_connect_userinfo_alter() must be of the type array, null given

Steps to reproduce

Proposed resolution

Allow NULL for hook_openid_connect_userinfo_alter():

- function hook_openid_connect_userinfo_alter(array &$userinfo, array $context) {
+ function hook_openid_connect_userinfo_alter(?array &$userinfo, array $context) {

or make sure that $userinfo is array:

    // Drupal\openid_connect\OpenIDConnect::buildContext()
    if ($plugin->usesUserInfo()) {
-      $userinfo = $plugin->retrieveUserInfo($tokens['access_token']);
+      $userinfo = $plugin->retrieveUserInfo($tokens['access_token']) ?: [];
    }

Remaining tasks

n/a

User interface changes

n/a

API changes

n/a

Data model changes

n/a