Using Reusable Blocks in the customizer / widgets

[robindevitt]

When creating a new Reusable block and wanting to use it in a widget, when adding the block you are presented with an error.

This block has encountered an error and cannot be previewed.

Steps to reproduce:

1. Ensure you have a Reusable Block to work with.
2. Navigate to Appearance -> Widgets
3. Add a new Reusable Block to one of the widgets.
4. When you hover the block to make your selection, you are present with the error mentioned above.

Describe what you expected to see:

I would have expected that a Reusable Block can be used in a widget area without any errors.

Acceptance criteria:

• Adding a Reusable Block to the widget area without seeing any errors.