Add FGM ( Fine Grained Masking ) support

[cdn34dd]

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• [ ] Feature or bugfix MUST have appropriate tests
• [ ] Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• [ ] Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)
• [ ] If this PR is auto-generated, please make sure also to manually update the code related to the change