• string | null: Check whether it's ok to map "" to null
• enum | null: Add 'null' or "None" item to enum
• number | null: "" => null
• boolean | null: ?? I don't see this in vscode's core settings

Also, enum | boolean. Example:

"git.autoRepositoryDetection": {
    "type": [
        "boolean",
        "string"
    ],
    "enum": [
        true,
        false,
        "subFolders",
        "openEditors"
    ],