Fix matching of throws Javadoc tags (#976)

JabRef/jabref-koppor#716
jablib/src/main/java/org/jabref/logic/crawler/StudyRepository.java

Author: tsantalis

src/main/java/gr/uom/java/xmi/diff/UMLJavadocDiff.java

@@ -166,7 +166,7 @@ else if(tagBefore.isReturn() && tagAfter.isReturn()) {
 				}
 				else if(tagBefore.isThrows() && tagAfter.isThrows()) {
 					boolean match = processModifiedTags(tagBefore, tagAfter);
-					if(match) {
+					if(match && !throwsTagAlreadyMatchedWithSameType(tagAfter)) {
 						deletedToBeDeleted.add(tagBefore);
 						addedToBeDeleted.add(tagAfter);
 						Pair<UMLTagElement, UMLTagElement> pair = Pair.of(tagBefore, tagAfter);
@@ -235,6 +235,15 @@ else if(tagBefore.isSee() && tagAfter.isSee()) {
 		this.addedTags.addAll(addedTags);
 	}
 
+	private boolean throwsTagAlreadyMatchedWithSameType(UMLTagElement tagAfter) {
+		for(Pair<UMLTagElement, UMLTagElement> pair : commonTags) {
+			if(pair.getRight().equals(tagAfter) && pair.getLeft().getFragments().get(0).equals(pair.getRight().getFragments().get(0))) {
+				return true;
+			}
+		}
+		return false;
+	}
+
 	private void matchNestedTags(UMLTagElement tagBefore, UMLTagElement tagAfter) {
 		List<UMLTagElement> nestedTagsBefore = tagBefore.getNestedTags();
 		List<UMLTagElement> nestedTagsAfter = tagAfter.getNestedTags();