Omit missing params when writing request/notification messages

Fixes #655.

Author: pisv

org.eclipse.lsp4j.jsonrpc/src/main/java/org/eclipse/lsp4j/jsonrpc/json/adapters/MessageTypeAdapter.java

@@ -418,12 +418,11 @@ public void write(JsonWriter out, Message message) throws IOException {
 			writeId(out, requestMessage.getRawId());
 			out.name("method");
 			out.value(requestMessage.getMethod());
-			out.name("params");
 			Object params = requestMessage.getParams();
-			if (params == null)
-				writeNullValue(out);
-			else
+			if (params != null) {
+				out.name("params");
 				handleParameter(out, params, requestMessage.getMethod());
+			}
 		} else if (message instanceof ResponseMessage) {
 			final var responseMessage = (ResponseMessage) message;
 			out.name("id");
@@ -443,12 +442,11 @@ public void write(JsonWriter out, Message message) throws IOException {
 			final var notificationMessage = (NotificationMessage) message;
 			out.name("method");
 			out.value(notificationMessage.getMethod());
-			out.name("params");
 			Object params = notificationMessage.getParams();
-			if (params == null)
-				writeNullValue(out);
-			else
+			if (params != null) {
+				out.name("params");
 				handleParameter(out, params, notificationMessage.getMethod());
+			}
 		}
 
 		out.endObject();

org.eclipse.lsp4j/src/test/java/org/eclipse/lsp4j/test/services/JsonSerializeTest.xtend

@@ -792,6 +792,36 @@ class JsonSerializeTest {
 			}
 		''')
 	}
+
+    @Test
+    def void testNoRequestParams() {
+        val message = new RequestMessage => [
+            jsonrpc = "2.0"
+            id = "12"
+            method = MessageMethods.SHUTDOWN
+        ]
+        message.assertSerialize('''
+            {
+              "jsonrpc": "2.0",
+              "id": "12",
+              "method": "shutdown"
+            }
+        ''')
+    }
+
+    @Test
+    def void testNoNotificationParams() {
+        val message = new NotificationMessage => [
+            jsonrpc = "2.0"
+            method = MessageMethods.EXIT
+        ]
+        message.assertSerialize('''
+            {
+              "jsonrpc": "2.0",
+              "method": "exit"
+            }
+        ''')
+    }
 
 	@Test
 	def void testProgressCreate() {