The current "Add report to dashboard" modal dialog does not require a confirmation (click on a button), instead once a report is selected in the <select>, it currently adds a report and closes the modal immediately.
While this saves a click, it breaks the established paradigm (and user's expectation) of a modal dialog and how it works. Also, as soon as more options are added to this or any other modal, it will need a button to confirm anyway, potentially resulting in inconsistency between modals that require confirmation and some that don't.
While at it, we should also add a 'Cancel' button. This does the exact same as the closing "x" on the modal, but it is good practice and welcome UI redundancy.
As a general rule, every modal should have a button to confirm the action/configuration (primary button, or in case of destructive operations, danger button), and a Cancel button.