Steps to reproduce the issue

$app = JApplicationCms::getInstance();
$credentials = array(
'username'=>$username
'password'=>$password
);
$options = array('action'=>'core.login.site'); // Define options and suppress 'cannot access private section of this website' warning in Joomla Core
$app->login($credentials,$options);

Expected result

The user is logged in with no error messages or the call fails and returns false or throws an exception

Actual result

Joomla displays an error message: "Call to a member function get() on null" from the line "$app->login($credentials,$options);"
Attempting to use JApplication (via JFactory::getApplication()) instead of JApplicationCms results in the same error. JApplicationWeb, which is indicated as a replacement for JApplicationCms in the Joomla 3.6 API documentation simply does not have a login method. Attempting to use triggerEvent instead seems to do nothing, but I'll admit I've never used it before and could have done it incorrectly. I tried the following:

$app = JApplicationWeb::getInstance();
$credentials = array(
'username'=>$username
'password'=>$password
);
$app->triggerEvent('core.login.site',$credentials)

System information (as much as possible)

PHP Built On Linux jbdev01 3.10.0-514.6.1.el7.x86_64 #1 SMP Wed Jan 18 13:06:36 UTC 2017 x86_64
Database Version 5.5.52-MariaDB
Database Collation utf8_general_ci
Database Connection Collation utf8mb4_general_ci
PHP Version 7.0.16
Web Server Apache/2.4.6 (CentOS) OpenSSL/1.0.1e-fips mod_fcgid/2.3.9 PHP/7.0.16
WebServer to PHP Interface apache2handler

The Joomla install was freshly updated from 3.6.5 to 3.7.0 with nothing else changed. The code worked perfectly well before the update.

Additional comments

I'm not really familiar with how Joomla authentication works beyond what I researched for our plugin-turned-component, so I'm afraid I don't know how to pursue this without dedicating significant research time to it (which I don't have, given my other projects).