The length of the map is longer than the number of bones the skeleton it is being assigned to actually has, causing array out of bounds error during generation
The length of the map is the correct length, but it is missing BoneTreeIndex entries (in any order) that is causing array index to be shorter than it should
Another thing to note: it is OK if the map is out of order.
There are 2 edge cases with this:
Another thing to note: it is OK if the map is out of order.