Created attachment 10480 [details]
According to https://msdn.microsoft.com/en-us/library/ms692727.aspx this function should return a valid pointer to a zero-length item.
Run the attached reproduction case and view the device console to see "Unexpected: Got null pointer from AllocCoTaskMem(0)"
This comes directly from the mono runtime we embed.
Fixed in mono master/mono-4.0.0-branch.
Fix back ported into maccore/master 49dda372a8c3d1564e82d45cdbfe4fa4c0c264b7
and maccore/macios-cycle5 8c5fc7ad854c2a712c1062b19820be4a45a41aee
IOW XI 8.10 will have this fix.