diff --git a/hapi-fhir-docs/src/main/resources/ca/uhn/hapi/fhir/changelog/5_2_0/2150-inmemory-null-source.yaml b/hapi-fhir-docs/src/main/resources/ca/uhn/hapi/fhir/changelog/5_2_0/2150-inmemory-null-source.yaml
new file mode 100644
index 00000000000..9b0472a0efb
--- /dev/null
+++ b/hapi-fhir-docs/src/main/resources/ca/uhn/hapi/fhir/changelog/5_2_0/2150-inmemory-null-source.yaml
@@ -0,0 +1,5 @@
+---
+type: fix
+issue: 2150
+title: "The In Memory search matcher (used for Subscriptions) could crash if a subscription was registered using the
+  `_source` search parameter, and a resource was processed with no source value. This has been corrected."
diff --git a/hapi-fhir-jpaserver-searchparam/src/main/java/ca/uhn/fhir/jpa/searchparam/util/SourceParam.java b/hapi-fhir-jpaserver-searchparam/src/main/java/ca/uhn/fhir/jpa/searchparam/util/SourceParam.java
index 938fcf6cb99..9ff5a50b881 100644
--- a/hapi-fhir-jpaserver-searchparam/src/main/java/ca/uhn/fhir/jpa/searchparam/util/SourceParam.java
+++ b/hapi-fhir-jpaserver-searchparam/src/main/java/ca/uhn/fhir/jpa/searchparam/util/SourceParam.java
@@ -2,6 +2,7 @@ package ca.uhn.fhir.jpa.searchparam.util;
 
 import ca.uhn.fhir.rest.api.Constants;
 
+import static org.apache.commons.lang3.StringUtils.defaultString;
 import static org.apache.commons.lang3.StringUtils.left;
 
 /*
@@ -35,19 +36,19 @@ public class SourceParam {
 	private final String myRequestId;
 
 	public SourceParam(String theParameterValue) {
-		myParameterValue = theParameterValue;
+		myParameterValue = defaultString(theParameterValue);
 		String requestId;
-		int lastHashValueIndex = theParameterValue.lastIndexOf('#');
+		int lastHashValueIndex = myParameterValue.lastIndexOf('#');
 		if (lastHashValueIndex == -1) {
-			mySourceUri = theParameterValue;
+			mySourceUri = myParameterValue;
 			requestId = null;
 		} else {
 			if (lastHashValueIndex == 0) {
 				mySourceUri = null;
 			} else {
-				mySourceUri = theParameterValue.substring(0, lastHashValueIndex);
+				mySourceUri = myParameterValue.substring(0, lastHashValueIndex);
 			}
-			requestId = theParameterValue.substring(lastHashValueIndex + 1);
+			requestId = myParameterValue.substring(lastHashValueIndex + 1);
 		}
 		myRequestId = left(requestId, Constants.REQUEST_ID_LENGTH);
 	}
diff --git a/hapi-fhir-jpaserver-searchparam/src/test/java/ca/uhn/fhir/jpa/searchparam/matcher/InMemoryResourceMatcherR5Test.java b/hapi-fhir-jpaserver-searchparam/src/test/java/ca/uhn/fhir/jpa/searchparam/matcher/InMemoryResourceMatcherR5Test.java
index e2cd7844f88..13d46785602 100644
--- a/hapi-fhir-jpaserver-searchparam/src/test/java/ca/uhn/fhir/jpa/searchparam/matcher/InMemoryResourceMatcherR5Test.java
+++ b/hapi-fhir-jpaserver-searchparam/src/test/java/ca/uhn/fhir/jpa/searchparam/matcher/InMemoryResourceMatcherR5Test.java
@@ -50,6 +50,7 @@ public class InMemoryResourceMatcherR5Test {
 	private static final String SOURCE_URI = "urn:source:0";
 	private static final String REQUEST_ID = "a_request_id";
 	private static final String TEST_SOURCE = SOURCE_URI + "#" + REQUEST_ID;
+
 	@MockBean
 	ISearchParamRegistry mySearchParamRegistry;
 	@Autowired
@@ -100,6 +101,27 @@ public class InMemoryResourceMatcherR5Test {
 		}
 	}
 
+	@Test
+	public void testSupportedSource_ResourceWithNoSourceValue() {
+		myObservation.getMeta().getSourceElement().setValue(null);
+		{
+			InMemoryMatchResult result = myInMemoryResourceMatcher.match(Constants.PARAM_SOURCE + "=" + TEST_SOURCE, myObservation, mySearchParams);
+			assertFalse(result.matched());
+		}
+		{
+			InMemoryMatchResult result = myInMemoryResourceMatcher.match(Constants.PARAM_SOURCE + "=" + SOURCE_URI, myObservation, mySearchParams);
+			assertFalse(result.matched());
+		}
+		{
+			InMemoryMatchResult result = myInMemoryResourceMatcher.match(Constants.PARAM_SOURCE + "=" + REQUEST_ID, myObservation, mySearchParams);
+			assertFalse(result.matched());
+		}
+		{
+			InMemoryMatchResult result = myInMemoryResourceMatcher.match(Constants.PARAM_SOURCE + "=#" + REQUEST_ID, myObservation, mySearchParams);
+			assertFalse(result.matched());
+		}
+	}
+
 	@Test
 	public void testUnsupportedChained() {
 		InMemoryMatchResult result = myInMemoryResourceMatcher.match("encounter.class=FOO", myObservation, mySearchParams);
diff --git a/hapi-fhir-jpaserver-subscription/src/main/java/ca/uhn/fhir/jpa/subscription/match/matcher/subscriber/MatchingQueueSubscriberLoader.java b/hapi-fhir-jpaserver-subscription/src/main/java/ca/uhn/fhir/jpa/subscription/match/matcher/subscriber/MatchingQueueSubscriberLoader.java
index 22ce2310775..72912f50234 100644
--- a/hapi-fhir-jpaserver-subscription/src/main/java/ca/uhn/fhir/jpa/subscription/match/matcher/subscriber/MatchingQueueSubscriberLoader.java
+++ b/hapi-fhir-jpaserver-subscription/src/main/java/ca/uhn/fhir/jpa/subscription/match/matcher/subscriber/MatchingQueueSubscriberLoader.java
@@ -4,11 +4,9 @@ import ca.uhn.fhir.jpa.subscription.channel.api.IChannelReceiver;
 import ca.uhn.fhir.jpa.subscription.channel.subscription.SubscriptionChannelFactory;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
-import org.springframework.beans.factory.DisposableBean;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.context.event.ContextRefreshedEvent;
 import org.springframework.context.event.EventListener;
-import org.springframework.messaging.SubscribableChannel;
 
 import javax.annotation.PreDestroy;
 
@@ -35,8 +33,8 @@ import static ca.uhn.fhir.jpa.subscription.match.matcher.subscriber.Subscription
  */
 
 public class MatchingQueueSubscriberLoader {
+	protected IChannelReceiver myMatchingChannel;
 	private Logger ourLog = LoggerFactory.getLogger(MatchingQueueSubscriberLoader.class);
-
 	@Autowired
 	private SubscriptionMatchingSubscriber mySubscriptionMatchingSubscriber;
 	@Autowired
@@ -46,8 +44,6 @@ public class MatchingQueueSubscriberLoader {
 	@Autowired
 	private SubscriptionActivatingSubscriber mySubscriptionActivatingSubscriber;
 
-	protected IChannelReceiver myMatchingChannel;
-
 	@EventListener(classes = {ContextRefreshedEvent.class})
 	public void handleContextRefreshEvent() {
 		if (myMatchingChannel == null) {