NullPointerException in mouseClicked handler when pressing "Cancel" on "Create New World" screen

Steps to reproduce:

1. Launch the Minecraft client (version 25w34b).

2. Select "Single Player" from the main menu.

3. Click "Create a new world".

4. On the "Create a new World" screen, immediately press the "Cancel" button.

5. The game will exit with a NullPointerException error.

Expected result:
The game should return to the single player world list screen or to the main menu without glitches.

The actual result:
The game crashes on the desktop with a fatal error.

(Optional) Additional remarks:

• The crash happens constantly every time I perform these actions.

• It doesn't matter if I change any world settings before pressing the Cancel button.