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<https://docs.gradle.org/current/userguide/incremental_build.html#sec:task_input_output_validation>:
&gt; [...]
&gt; it does the following for each property before the task executes:
&gt; [...]
&gt; • `@OutputDirectory` - verifies that the path doesn’t match a file and also creates the directory if it doesn’t already exist.


I don't know why `@Optional` should have any influence.
`@Optional` on an input file or directory property does *not* mean you can configure a non-existing path.
It means that you are allowed to not configure it, but if you configure it, it must exist (when an input)

I had an `@OutputDirectory` annotated with `@Optional`, and set it, expecting the directory to exist, only to encounter an error stating that it didn't.

I just tried with this complete build script:
```abstract class Foo : DefaultTask() {
    @get:Optional
    @get:OutputDirectory
    abstract val out: DirectoryProperty

    @TaskAction
    fun foo() = Unit
}

val foo by tasks.registering(Foo::class) {
    out = layout.buildDirectory.dir("foo")
}```
When I executed the `foo` task, the directory was created as expected.

I wonder if there are any complications relating to `@Nested` output properties, then? On paper, it shouldn't, but, barring external factors, I don't see why an `@OutputDirectory` property would fail to create the directory. (Maybe nested directories? Hard to say.)

Worst case, it's probably something that can be worked around.

Also this works fine:
```interface Bar {
    @get:OutputDirectory
    val out: DirectoryProperty
}

abstract class Foo : DefaultTask() {
    @get:Nested
    abstract val bar: Bar

    @TaskAction
    fun foo() = Unit
}

val foo by tasks.registering(Foo::class) {
    bar.out = layout.buildDirectory.dir("foo")
}```
