A SUPPORTED_PARAMETERS response with a PDL of 0x00 is really a corner case. Most of the time you won't need it.
Arguably you could respond with 0x00 if you don't support any of the optional PIDs.
Also, there might be situations where you want to Queue a SUPPORTED_PARAMETERS response. For example, if the user does something at the responder's local menu that causes it to change the set of PIDs it supports.
Don't read too much in to it... Nearly ever real-world responder will have a non-zero length response to GET SUPPORTED_PARAMETERS. Controllers should probably not crash if they get a response with a PDL of zero, but you won't see it very often.
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