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I think you can return `null`  which is the value for "not set"

The doc is very explicit that the callback should not return `null`

Wait, I'm on a super old version of Gradle actually where the symbol was still Incubating, let me check recent ones

:thinking_face: The doc says:

```The provider is live and will call the {@link Callable} each time its value is queried. The {@link Callable} may return {@code null}, in which case the provider is considered to have no value.  ```

Right, it changed when the API became stable, I have this too now

Time to update my minGradleVersion :slightly_smiling_face:

<https://github.com/gradle/gradle/issues/19981>