resolveDebugConfiguration returning 'undefined' or 'null' does not comply to vscode API

[alvsan09]

Bug Description:

The vscode plugin ms-vscode.js-debug provides a dynamic configuration called Create Java Debug Terminal
which does not actually require a session, it simply opens a terminal as a side effect of starting it, and when the extension
provider is called with resolveDebugConfiguration the extension simply returns undefined to indicate that no further processing is required.

This is expected as specified: https://code.visualstudio.com/api/references/vscode-api#DebugConfigurationProvider

Theia currently ignores undefined or null, and starts the session using the configuration in place before an undefined or null is returned.

Steps to Reproduce:

As it can be seen in the gif below this case starts a session with a corresponding terminal in addition to the terminal triggered by the extension.

1. Open the command palette and type debug , not the ending space is important
2. Select Create JavaScript Debug terminal from the list of available configurations
3. See that a Session and corresponding terminal is started in addition to a JavaScript Debug Terminal

Additional Information

• Operating System: Ubuntu
• Theia Version: 1.24.0