Temporarily don't require a dependent capability to register a runtime-only requirement

Temporarily allow the "dependent" param to OperationContext.hasOptionalCapability to be null. Don't change the method javadoc which says it cannot be null. Just be forgiving in the actual implementation.

This will allow code that wants to use a capability if present to do so without itself being a capability. The downside to this is we won't be able to record the fact that that code is using the capability and present that info to users via the management API. (For example, a user may want to know that kind of thing when performing a slimming exercise.)

This will allow dependent code that doesn't have its own set of capabilities worked out to still use runtime-only requirements anyway.

This "forgiveness" is only applicable to runtime-only requirements, which are defined as those where the requiring code has nothing in its configuration model that says the required capability must be present. Other kinds of registered requirements mean the config is incorrect if the required capability is removed, so we must have the information as to what the requiring capability is so we can properly report the error.