NullReferenceException in Terms Parsing

[Enkidu93]

We recently got this error on production:

System.NullReferenceException: Object reference not set to an instance of an object.
         at System.Linq.Lookup`2.Create[TSource](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)
         at System.Linq.GroupedEnumerable`3.GetEnumerator()
         at System.Linq.Enumerable.SelectEnumerableIterator`2.MoveNext()
         at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)
         at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector)
         at SIL.Machine.Corpora.ParatextProjectTermsParserBase.Parse(IEnumerable`1 termCategories, Boolean useTermGlosses)

Unfortunately, we don't have line numbers for the Machine code so it's not clear which ToDictionary is causing this. It's possible that it's getting a null gloss value from the xml(?).

[johnml1135]

I can't find the build on the server, or the database - 66e4aeeae234a38f4faa59b3.

My best guess for a resolution is to have both "SelectsMany" calls above the ToDictionary have a null coalescing because this is .netstandard2.0 and has no explicit null checking enforcement.

Still, we should create dummy data to recreate the failure and have the code change fix it.

[johnml1135]

I can't recreate the error. I'm passing on this until we get better data.