Fix <RichTextField> should render emptyText when value is an empty string

[slax57]

Problem

<RichTextField> does not render emptyText when the value is equal to ''.

Solution

Fix <RichTextField> to render emptyText when the value is an empty string.

How To Test

Unit test + new Story

Additional Checks

• The PR targets master for a bugfix or a documentation fix, or next for a feature
• The PR includes unit tests (if not possible, describe why)
• The PR includes one or several stories (if not possible, describe why)
• The documentation is up to date

Also, please make sure to read the contributing guidelines.

[djhi]

👍