LTI launches with errors if custom parameters are set

In Moodle 3.8 when an external tool is launched with custom_parameters (eg force_embed=1) the following error is currently produced, before it does finally launch.

Trying to get property of non-object at .../mod/lti/locallib.php on line 1829

It appears to be a regression of :
https://tracker.moodle.org/browse/MDL-60415

To reproduce this:

1. Create a new external tool
2. Enter the cartrige URL for a course that has been published as LTI
3. Enter the secret matching that cartridge URL
4. Choose to open the launched tool in a new window
5. Set custom parameter: force_embed=1
6. When you launch the LTI activity and debugging is sending output to screen , then you will see the above error flash by en-route to the application loading