Error when trying to cancel window closure with an open project

[soaressgabriel]

Describe the bug
When trying to close the window with an open, changed and unsaved project, a dialog box opened to confirm the operation, I clicked the Cancel button and an error occurred.

To Reproduce
Steps to reproduce the behavior:

1. Go to Plugins > RUBEM Hydrological > RUBEM Hydrological;
2. Click on New;
3. Do not save the project;
4. Insert or change any field;
5. Close the plugin window;
6. Click the Cancel button in the message box that appears;
7. See the error (qgis-error-msg.txt).

Expected behavior
When trying to close the window with an open, changed and unsaved project, a dialog box opened to confirm the operation, click the Cancel button and the operation is cancelled.

Desktop (please complete the following information):

• OS: Windows 11 21H2
• Version: v1.11.15-03122021-alpha