fix: NullPointerException in the 'insertCommentInAST' method for an empty switch statement. (INRIA#3191)

Author: BuzzMS

src/main/java/spoon/support/compiler/jdt/JDTCommentBuilder.java

@@ -372,7 +372,7 @@ public <E> void visitCtSwitch(CtSwitch<E> e) {
 					}
 					previous = ctCase;
 				}
-				if (previous.getPosition().getSourceEnd() < comment.getPosition().getSourceStart()) {
+				if (previous != null && previous.getPosition().getSourceEnd() < comment.getPosition().getSourceStart()) {
 					addCommentToNear(comment, new ArrayList<>(previous.getStatements()));
 					try {
 						comment.getParent();

src/test/java/spoon/test/comment/CommentTest.java

@@ -1120,17 +1120,23 @@ public void testCommentGetRawContent() {
 				" * @version 1.0\r" + 
 				" */", type.getComments().get(0).getRawContent());
 	}
+
 	@Test
 	public void testEmptyStatementComments() {
 		//contract: model building should not produce NPE, comments should exist
 		Launcher launcher = new Launcher();
 		launcher.addInputResource("./src/test/java/spoon/test/comment/testclasses/EmptyStatementComments.java");
 		launcher.getEnvironment().setCommentEnabled(true);
 
-		CtModel model = launcher.buildModel();
-		List<CtIf> conditions = model.getElements(new TypeFilter<>(CtIf.class));
+		List<CtMethod<?>> methods = launcher.buildModel().getElements(new TypeFilter<>(CtMethod.class));
+
+		List<CtIf> conditions = methods.get(0).getElements(new TypeFilter<>(CtIf.class));
 		assertEquals("comment", conditions.get(0).getComments().get(0).getContent());
 		assertEquals("comment", conditions.get(1).getComments().get(0).getContent());
+
+		List<CtSwitch<?>> switches = methods.get(1).getElements(new TypeFilter<>(CtSwitch.class));
+		assertEquals("commentInline", switches.get(0).getComments().get(0).getContent());
+		assertEquals("commentBlock", switches.get(1).getComments().get(0).getContent());
 	}
 
 	@Test

src/test/java/spoon/test/comment/testclasses/EmptyStatementComments.java

@@ -8,4 +8,14 @@ void m1() {
         if (true) /* comment */
             ;
     }
+
+    void m2(int value) {
+        switch (value) {
+            // commentInline
+        }
+
+        switch (value) {
+            /* commentBlock */
+        }
+    }
 }