Pressing the arrow down key on the keyboard, causes SuggestBox to throw an Exception

[FrankW76]

Describe the bug
When you have SuggestBox.
Give it focus.
Press down on the keyboard. An Exception will appear.

This is because arrow down will try to select the next item in the dropdown. But the dropdown is not yet available at that moment.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://demo.dominokit.org/forms/advanced-form-elements
2. Open the developer tools of your browser, and open the console
3. On this page you can find a SuggestBox with a label : Your friends
4. Click on this SuggestBox to give it focus
5. Now press the 'arrow down' key of your keyboard
6. An Exception will appear in the develor tools console (Cannot read properties of undefined)

The problem with above is, that we use an 'uncaughtExceptionHandler' in our own app. Which shows a big error for all these errors. And thus every time a user tries above steps, he gets a big error dialog.

Expected behavior
Do not throw an exception

Screenshots

Desktop (please complete the following information):

• OS: Windows
• Browser Chrome
• Version Latest

[FrankW76]

DropDownMenu.java

Modify the focus method to below code, will fix this issue.

public void focus() { if (keyboardNavigation != null) keyboardNavigation.focusAt(0); }