i2b2 webclient error: failed login; message, "The PM Cell is down or the address in the properties file is incorrect"

# To reproduce:
- on macOS:
    - install i2b2 database (postgres)
    - install i2b2 demo data (sql)
    - install core i2b2 server (jboss)
    - install i2b2 webclient (php)
    - login to local i2b2 webclient (error below)

# Trace to debug
Error: Undefined array key \"query\" in <b>/opt/local/www/apache2/html/proxy.php</b> on line <b>115</b>

# Bug location
// /opt/local/www/apache2/html/proxy.php
$sec_fix = parse_url($proxyURL);
// $sec_fix = [scheme: http, host: localhost, port: 9090, path: /i2b2/services/PMService/getServices]
if ($sec_fix['query'] != null) { // 115
}

# identify issue
// output $sec_fix
foreach ($sec_fix as $key => $value) {
    echo "$key: $value; ";
}
/*
[scheme: http, host: localhost, port: 9090, path: /i2b2/services/PMService/getServices]
*/

# apply fix
// fix: option 1
//if (isset($sec_fix['query']) && $sec_fix['query'] != null) {
// $proxyURL = $proxyURL . "?" . $sec_fix['query'];
//}

// fix: option 2
if (array_key_exists('query', $sec_fix)) {
    if ($sec_fix['query'] != null) {
        $proxyURL = $proxyURL . "?" . $sec_fix['query'];
    }
}

After fix is applied to proxy.php, the i2b2 webclient login works.