eclipse-archived/xtext-core#558: Always write a null value into message body

Author: spoenemann

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

@@ -287,7 +287,7 @@ public void write(JsonWriter out, Message message) throws IOException {
 			out.name("params");
 			Object params = requestMessage.getParams();
 			if (params == null)
-				out.nullValue();
+				writeNullValue(out);
 			else
 				gson.toJson(params, params.getClass(), out);
 		} else if (message instanceof ResponseMessage) {
@@ -301,7 +301,7 @@ public void write(JsonWriter out, Message message) throws IOException {
 				out.name("result");
 				Object result = responseMessage.getResult();
 				if (result == null)
-					out.nullValue();
+					writeNullValue(out);
 				else
 					gson.toJson(result, result.getClass(), out);
 			}
@@ -312,12 +312,22 @@ public void write(JsonWriter out, Message message) throws IOException {
 			out.name("params");
 			Object params = notificationMessage.getParams();
 			if (params == null)
-				out.nullValue();
+				writeNullValue(out);
 			else
 				gson.toJson(params, params.getClass(), out);
 		}
 
 		out.endObject();
 	}
 
+	/**
+	 * Use this method to write a {@code null} value even if the JSON writer is set to not serialize {@code null}.
+	 */
+	protected void writeNullValue(JsonWriter out) throws IOException {
+		boolean previousSerializeNulls = out.getSerializeNulls();
+		out.setSerializeNulls(true);
+		out.nullValue();
+		out.setSerializeNulls(previousSerializeNulls);
+	}
+	
 }

org.eclipse.lsp4j.jsonrpc/src/test/java/org/eclipse/lsp4j/jsonrpc/test/IntegrationTest.java

@@ -344,8 +344,8 @@ public CompletableFuture<MyParam> askServer(MyParam param) {
 			logMessages.await(Level.INFO, "Unsupported notification method: $/foo1");
 			logMessages.await(Level.INFO, "Unsupported request method: $/foo2");
 
-			Assert.assertEquals("Content-Length: 26" + CRLF + CRLF
-					+ "{\"jsonrpc\":\"2.0\",\"id\":\"1\"}",
+			Assert.assertEquals("Content-Length: 40" + CRLF + CRLF
+					+ "{\"jsonrpc\":\"2.0\",\"id\":\"1\",\"result\":null}",
 					out.toString());
 		} finally {
 			logMessages.unregister();

org.eclipse.lsp4j/src/test/java/org/eclipse/lsp4j/test/services/NullResponseTest.java

@@ -47,7 +47,7 @@ public class NullResponseTest implements LanguageServer {
 		request.setId("1");
 		request.setMethod("shutdown");
 		re.consume(request);
-		Assert.assertEquals("{\"jsonrpc\":\"2.0\",\"id\":\"1\"}", handler.serialize(msgs.get(0)));
+		Assert.assertEquals("{\"jsonrpc\":\"2.0\",\"id\":\"1\",\"result\":null}", handler.serialize(msgs.get(0)));
 		msgs.clear();
 		shutdownReturn = new Object();
 		re.consume(request);