Address compiler warnings

Core/Parsers/AssignmentRequirementParser.cs

@@ -15,7 +15,7 @@ public class AssignmentRequirementParser : CsvParserBase
 		CsvReader.Read();
 		CsvReader.ReadHeader();
 		var studentColumns =
-			CsvReader.HeaderRecord.Select(h => h.Trim()).Where(h => !string.IsNullOrEmpty(h)).ToArray();
+			CsvReader.HeaderRecord!.Select(h => h.Trim()).Where(h => !string.IsNullOrEmpty(h)).ToArray();
 
 		var studentArray = 
             studentColumns
@@ -30,21 +30,25 @@ public class AssignmentRequirementParser : CsvParserBase
 				throw new Exception($"Could not find eventDefinition named {eventShortName}");
 			for (int i = 0; i <= studentArray.Length; i++)
 			{
+				var student = studentArray[i];
+				if (student == null)
+					continue;
+
 				var field = CsvReader.GetField(i + 1);
 				switch (field)
 				{
 					case "x":
 					case "X":
-						assumptions.Add(new AssignmentRequirement(evt, studentArray[i], Requirement.Exclude));
+						assumptions.Add(new AssignmentRequirement(evt, student, Requirement.Exclude));
 						break;
 					case "i":
 					case "I":
-						assumptions.Add(new AssignmentRequirement(evt, studentArray[i], Requirement.Include));
+						assumptions.Add(new AssignmentRequirement(evt, student, Requirement.Include));
 						break;
 					default:
 						break;
 				}
-				
+
 			}
 		}