When I chose "Heap Parameters" menu in HSDB, I got following value:
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Heap Parameters:
unknown subtype of CollectedHeap @ 0x00007f4d4c030510 (0x00000006c6e00000,0x00000007c0000000)
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I think it should not be "unknown subtype".

This value is shown by sun.jvm.hotspot.gc.shared.CollectedHeap#printOn().
This method is overrided in ParallelScavengeHeap and GenCollectedHeap. However, G1CollectedHeap does not override.

I think G1CollectedHeap should override this method.