I have an LTI 1.3 tool registered using deep linking/content selection. When I add a new activity using the tool, then Select Content, then select from the tool, I get an error from Moodle:

Exception - Argument 1 passed to params_to_string() must be an object, array given, called in [dirroot]/mod/lti/locallib.php on line 1576

The Apache log says:

PHP message: Default exception handler: Exception - Argument 1 passed to params_to_string() must be an object, array given, called in [dirroot]/mod/lti/locallib.php on line 1576 Debug: 
Error code: generalexceptionmessage

• line 1464 of /mod/lti/locallib.php: TypeError thrown
• line 1576 of /mod/lti/locallib.php: call to params_to_string()
• line 1629 of /mod/lti/locallib.php: call to content_item_to_form()
• line 84 of /mod/lti/contentitem_return.php: call to lti_tool_configuration_from_content_item()
  ', referer: https://[redacted]/

This did not happen in 4.0, only since switching to v4.1.1.

To reproduce:

1. Set up a Moodle-to-Moodle LTI using LTI Advantage (See the first few sections of MDL-78219's testing instructions if you're not sure how this is done. Also, docs if needed). You'll need one published activity - published over LTI 1.3.
2. Apply this patch to the TOOL site: https://github.com/snake/moodle/compare/580c009cacb...MDL-77249-replication-deeplinkresponse. This just forced an empty object within the deep link response JSON.

   git pull https://github.com/snake/moodle MDL-77249-replication-deeplinkresponse

3. In the PLATFORM site, click to create an activity
4. Select the Moodle tool
5. Select the activity checkbox and click "Add content"
   Expected: The modal closes without error, and you see the activity instance form is updated with details of the activity (e.g. name)
   Actual: You'll see an exception in the modal:

   Exception - params_to_string(): Argument #1 ($params) must be of type object, array given, called in [dirroot]/mod/lti/locallib.php on line 1503