Null Reference in Coroutine only accessing floats and method calls

We have received 4 crash reports for our mobile game from hockeyapp with the following null reference error in a coroutine:

NullReferenceException: Object reference not set to an instance of an object
at RenderQueueOverride+<crUpdateQueue>c__IteratorC5.MoveNext ()

The coroutine in question is started in OnEnable and only makes method calls, starts other coroutines, or accesses a float parameter so I'm really not sure what could be causing the null reference. Here is the coroutine in question:

Code (CSharp):

1.     float m_UpdateInterval = 1f;
2.  
3.     IEnumerator crUpdateQueue()
4.     {
5.         yield return null;
6.         yield return null;
7.  
8.         UpdateRenderQueue();
9.         yield return StartCoroutine(crWaitRealtimeSeconds(0.1f));
10.  
11.         for (;;)
12.         {
13.             UpdateRenderQueue();
14.             yield return StartCoroutine(crWaitRealtimeSeconds(m_UpdateInterval));
15.         }
16.     }

Any ideas what could be causing this exception?

 

Perhaps you can get that error also if something goes wrong in crWaitRealtimeSeconds (returning a null?)

 

Here's crWaitRealtimeSeconds but I don't see anything obvious there either. Can the unity Time class be null?

Code (CSharp):

1.     IEnumerator crWaitRealtimeSeconds(float waitTime)
2.     {
3.         float startTime = Time.realtimeSinceStartup;
4.         float endTime = startTime + waitTime;
5.         while (Time.realtimeSinceStartup < endTime)
6.         {
7.             yield return null;
8.         }
9.     }

 

Since realtimeSinceStartup don't stop when you pause the game, it could happen that after a pause the coroutine ends before the expected time, so calling UpdateRenderQueue() again possibly too soon. I don't know if it's possible that UpdateRenderQueue() could be called again before it ends and what are the implications of that...