HTTP ERROR 400 Bad argument error when clicking "Add" button with an empty query

Steps to reproduce

1. Go to own user profile
2. Click on "Word-Based Notification" tab
3. Without inserting any query, click "Add" button

Expected result

A small red warning is displayed under the "Insert New Query" input field saying maybe: "This field is mandatory".

Actual results

The user is directed to a HTTP 400 Error:

HTTP ERROR 400 Bad argument

URI:/xwiki/bin/view/XWiki/Admin
STATUS:400
MESSAGE:Bad argument
SERVLET:action 

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In my opinion, either:

• the warning message should be displayed when the "Add" button is clicked with an empty box (prior executing the action)
• the "Add" button should be disabled (greyed out) altogether until something is inserted in the box