Minor Description
In InfosetImpl, DIComplex and DIArrays have arrays of child elements. To reduce memory usage, Daffodil will set some of these array indices to null to if we determine that they will never be accessed again. Unfortunately, this means that if there is a bug in Daffodil and it does get accessed then we'll get a NullPointerException. We should refactor this code to avoid potential NPE's, likely by changing these array contents to Maybe's.