Unclear message when ValueSource parameters are accessed for a source with None parameters

[alllex]

Consider the following snippet:

abstract class MyValueSource : ValueSource<String, ValueSourceParameters.None> {
    override fun obtain(): String? {
        println("Parameters: $parameters")
        return "foo"
    }
}

This currently fails with:

> org.gradle.internal.service.UnknownServiceException: No service of type ValueSourceParameters$None available in value source services.
  > No service of type ValueSourceParameters$None available in value source services.

There seems to be no contract for accessing the parameters for a value source that has ValueSourceParameters.None, e.g. in any of the javadocs.

It is currently forbidden by failing, but there seems to be no reason why this shouldn't be supported.

There are at least two use-cases:

• A user was experimenting and reduced their parameters to None without updating the implementation code that still accesses the parameters
• A user has an abstract value source class that prints parameters for debugging. It should not matter whether children of this class use ValueSourceParameters.None as a parameter type.

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Build scan: https://ge.gradle.org/s/yxps2f3m5husm/failure#1

[alllex]

We have other Parameters-like concepts, the UX for which should ideally be the same:

• WorkParameters have a javadoc contract about forbidding access to parameters, when they are None
• FlowParameters also explicitly forbids calling parameters when None, but the None instance of parameters seems to be passed to the flow action regardless.
• TransformParameters also forbids calling parameters when None

[mlopatkin]

This feature request is in the backlog of the relevant team and is prioritized by them.

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We should make all aforementioned places (and BuildServiceParameters) behave in the same way. Preferrably, we should allow getting None instances in both getParameters and when registering/configuring, just for simplicity of the contract.

[big-guy]

+1 for removing the specialness of None.