Issue Summary

When you have an Assets custom field configured to store multiple objects, you can only select the objects one by one.

Steps to Reproduce

1. Create an assets custom field and add it to one of your projects.
2. Go to your custom field configuration and select 'Field can store multiple objects'
3. Go to an issue that has the custom field and try to select multiple objects at once.

Expected Results

If the assets custom field is configured to allow for multiple objects you should be able to select multiple at once.

Actual Results

You need to select the objects for the custom field one by one.