SAM-2717 - Handle copy of null grading attachments

There is a setter for the grading attachment list on
AssessmentGradingData, which wraps an underlying HashSet. When copying,
for example, from AgentResults, where there are no attachments, the
HashSet constructor on the null value throws an
InvocationTargetException, which obscured the problem. This change
creates a new, empty set if null is passed to this setter.

samigo/samigo-api/src/java/org/sakaiproject/tool/assessment/data/dao/grading/AssessmentGradingData.java

@@ -452,7 +452,14 @@ public List<AssessmentGradingAttachment> getAssessmentGradingAttachmentList() {
 
 	public void setAssessmentGradingAttachmentList(
 			List<AssessmentGradingAttachment> assessmentGradingAttachmentList) {
-		Set<AssessmentGradingAttachment> assessmentGradingAttachmentSet = new HashSet<AssessmentGradingAttachment>(assessmentGradingAttachmentList);
+		Set<AssessmentGradingAttachment> assessmentGradingAttachmentSet = null;
+
+		if (assessmentGradingAttachmentList != null) {
+			assessmentGradingAttachmentSet = new HashSet<AssessmentGradingAttachment>(assessmentGradingAttachmentList);
+		} else {
+			assessmentGradingAttachmentSet = new HashSet<AssessmentGradingAttachment>();
+		}
+
 		this.assessmentGradingAttachmentSet = assessmentGradingAttachmentSet;
 	}