Added tests for null key handling in DictionaryExtensions#498

siriak merged 3 commits intoTheAlgorithms:masterTheAlgorithms/C-Sharp:masterfrom

gmottajr:feature/Issue-465_CoverageForHashTableAndTimSortergmottajr/C-Sharp:feature/Issue-465_CoverageForHashTableAndTimSorterCopy head branch name to clipboard