[BUG] expression object is filled with default values

[igarashitm]

Describe the bug
A variation of #503

expression object is filled with default values after code sync

To Reproduce
Steps to reproduce the behavior:

1. Open source code editor
2. Paste this code

- from:
    uri: timer:null
    steps:
      - choice:
          when:
            - expression:
                simple:
                  expression: choice

4. Click sync your code
5. YAML is updated with default values

- from:
    uri: timer:null
    steps:
    - choice:
        when:
        - expression:
            simple:
              expression: choice
              trim: false
              result-type: 'null'
              id: 'null'
          steps: []

Expected behavior
Default values are wiped out

Logs
If applicable, add logs to help explain your problem.

Environment (please complete the following information):

• OS: [e.g. "Linux 5.10.0-9-amd64 Using sonarcloud action to add details on PR #1 SMP Debian 5.10.70-1 (2021-09-30) x86_64 GNU/Linux"]
• Output of the mvn -version` command
• Kaoto Version [e.g. 1.0]

Additional context
Add any other context about the problem here.

[igarashitm]

It looks nasty, not sure if default values are even accessible for sub properties of object property... even worse is that at some point the property value is converted from null to a String literal "null"