Fix for #5773 (#5774)

* Breaking test and null check

* Changelog

hapi-fhir-docs/src/main/resources/ca/uhn/hapi/fhir/changelog/7_2_0/5773-fix-subscriptions-with-null-content-cause-null-pointer-exception.yml

@@ -0,0 +1,4 @@
+---
+type: fix
+issue: 5773
+title: "Subscriptions with null content caused NullPointerExceptions. This condition is now checked and handled."

hapi-fhir-jpaserver-subscription/src/main/java/ca/uhn/fhir/jpa/subscription/match/deliver/websocket/SubscriptionWebsocketHandler.java

@@ -205,6 +205,9 @@ public class SubscriptionWebsocketHandler extends TextWebSocketHandler implement
 		 * @return The payload
 		 */
 		private Optional<String> getPayloadByContent(ResourceDeliveryMessage msg) {
+			if (msg.getSubscription().getContent() == null) {
+				return Optional.empty();
+			}
 			switch (msg.getSubscription().getContent()) {
 				case IDONLY:
 					return Optional.of(msg.getPayloadId());

hapi-fhir-jpaserver-test-r5/src/test/java/ca/uhn/fhir/jpa/subscription/websocket/WebsocketWithSubscriptionIdR5Test.java

@@ -59,6 +59,36 @@ public class WebsocketWithSubscriptionIdR5Test extends BaseSubscriptionsR5Test {
 		myWebsocketClientExtension.afterEach(null);
 	}
 
+	@Test
+	public void testSubscriptionMessagePayloadContentIsNull() {
+		// Given a subscription
+		Subscription subscription = new Subscription();
+		subscription.setStatus(Enumerations.SubscriptionStatusCodes.ACTIVE);
+		subscription.setContent(null);
+		subscription.setTopic("Topic/123");
+		subscription.getChannelType().setCode("websocket");
+		MethodOutcome methodOutcome = myClient.create().resource(subscription).execute();
+		String subscriptionId = methodOutcome.getId().getIdPart();
+
+		// When
+		myWebsocketClientExtension.bind(subscriptionId);
+
+		// And
+		// Trigger resource creation
+		Patient patient = new Patient();
+		patient.setActive(true);
+		myClient.create().resource(patient).execute();
+
+		// Then
+		List<String> messages = myWebsocketClientExtension.getMessages();
+		await().until(() -> !messages.isEmpty());
+
+		// Log it
+		ourLog.info("Messages: {}", messages);
+
+		// Verify a ping message shall be returned
+		Assertions.assertTrue(messages.contains("ping " + subscriptionId));
+	}
 
 	@Test
 	public void testSubscriptionMessagePayloadContentIsEmpty() {