Missing email prevents metadata file update when pom.xml present

[GGoetzelmann]

Feel free to change the issue title to a more fitting description

Describe the bug
Under certain circumstances not providing an email prevents somesy from syncing files. It seems at least to be related to the existance of a pom.xml file and does not occur without it.

I would assume it should either not work at all, if mail would be a mandatory field (from other discussions I derived that it shouldn't be - and I would obviously agree with that, since I did not provide one in my file), or it should sync without email info.

To Reproduce
Steps to reproduce the behavior:

1. Create a project with a minimal pom.xml file and the following somesy.toml

    [project]
    name = "my-amazing-project"
    version = "0.1.0"
    description = "Brief description of my amazing software."
    
    keywords = ["some", "descriptive", "keywords"]
    license = "MIT"
    repository = "https://github.com/username/my-amazing-project"
    
    # This is you, the proud author of your project:
    [[project.people]]
    given-names = "Jane"
    family-names = "Doe"
    author = true      # is a full author of the project (i.e. appears in citations)
    maintainer = true  # currently maintains the project (i.e. is a contact person)
   

2. use somesy sync. This will work and correctly creates CITATION.cff etc.

3. Change Jane Doe's maintainer role from true to false in somesy.toml

4. use somesy sync again

Expected: somesy updates the metadata files.

Actual behaviour: somesy sync breaks after pom, therefore not updating files

After deleting the pom.xml, somesy sync works as expected

Synchronizing project metadata...
Files to sync:
  - pyproject.toml:     pyproject.toml
  - package.json:       package.json
  - Project.toml:       Project.toml

  - fpm.toml(fortran):  fpm.toml
  - pom.xml:    pom.xml

  - mkdocs.yml: mkdocs.yml
  - Cargo.toml: Cargo.toml
  - CITATION.cff:       CITATION.cff
  - codemeta.json:      codemeta.json


Synchronizing root project metadata...
Cannot validate POM file, skipping validation.
Error: 'email'

Screenshots

Traces

Environment

• somesy version: 0.7.3
• Python 3.12.0

Additional context