[Mono-dev] Mono 3.10.0 NullReferenceException in RBTree.find_key

[Sotirios Delimanolis]

Running Mono 3.10.0
Mono JIT compiler version 3.10.0 (tarball Fri Oct 10 17:29:39 UTC 2014)
We're seeing an unhandled exception that crashes our program in MemoryCache's scheduled cleanup . This is the stack trace dumped before exit
2017-06-22 03:14:28.478510 GMT Unhandled Exception:
2017-06-22 03:14:28.478511 GMT System.NullReferenceException: Object reference not set to an instance of an object
2017-06-22 03:14:28.478512 GMT   at System.Collections.Generic.RBTree.find_key[String] (System.String key, System.Collections.Generic.List`1 path) [0x00000] in <filename unknown>:0
2017-06-22 03:14:28.478514 GMT   at System.Collections.Generic.RBTree.Remove[String] (System.String key) [0x00000] in <filename unknown>:0
2017-06-22 03:14:28.478551 GMT   at System.Collections.Generic.SortedDictionary`2[System.String,System.Runtime.Caching.MemoryCacheEntry].Remove (System.String key) [0x00000] in <filename unknown>:0
2017-06-22 03:14:28.478553 GMT   at System.Runtime.Caching.MemoryCacheContainer.DoRemoveEntry (System.Runtime.Caching.MemoryCacheEntry entry, Boolean updateLRU, System.String key, CacheEntryRemovedReason reason) [0x00000] in <filename unknown>:0
2017-06-22 03:14:28.478557 GMT   at System.Runtime.Caching.MemoryCacheContainer.DoRemoveExpiredItems (Boolean needLock) [0x00000] in <filename unknown>:0
2017-06-22 03:14:28.478559 GMT   at System.Runtime.Caching.MemoryCacheContainer.RemoveExpiredItems (System.Object state) [0x00000] in <filename unknown>:0
2017-06-22 03:14:28.478562 GMT   at System.Threading.Timer+Scheduler.TimerCB (System.Object o) [0x00000] in <filename unknown>:0

Looking at the find_key implementation here, I don't see anything that can be null that could cause a NullReferenceException. 
What is going on?

 
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