fix #1711: add null check for headers, add a unit test (#1714)

spring-cloud-contract-verifier/src/main/java/org/springframework/cloud/contract/verifier/messaging/jms/JmsStubMessages.java

@@ -17,6 +17,7 @@
 package org.springframework.cloud.contract.verifier.messaging.jms;
 
 import java.io.Serializable;
+import java.util.Collections;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 
@@ -58,7 +59,7 @@ class JmsStubMessages implements MessageVerifier<Message> {
 	public void send(Object payload, Map headers, String destination, YamlContract contract) {
 		jmsTemplate.send(destination, session -> {
 			Message message = createMessage(session, payload);
-			setHeaders(message, headers);
+			setHeaders(message, headers == null ? Collections.emptyMap() : headers);
 			return message;
 		});
 	}

spring-cloud-contract-verifier/src/test/java/org/springframework/cloud/contract/verifier/messaging/jms/JmsStubMessagesTests.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright 2021-2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.contract.verifier.messaging.jms;
+
+import javax.jms.JMSException;
+import javax.jms.Session;
+import javax.jms.TextMessage;
+
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.mockito.ArgumentCaptor;
+
+import org.springframework.jms.core.JmsTemplate;
+import org.springframework.jms.core.MessageCreator;
+
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+public class JmsStubMessagesTests {
+
+	@Test
+	void should_send_message_without_headers_and_contract() throws JMSException {
+		final JmsTemplate jmsTemplate = mock(JmsTemplate.class);
+		final Session session = mock(Session.class);
+		final TextMessage message = mock(TextMessage.class);
+
+		when(session.createTextMessage(anyString())).thenReturn(message);
+
+		final JmsStubMessages springJmsStubMessages = new JmsStubMessages(jmsTemplate);
+
+		springJmsStubMessages.send(anyString(), null, anyString(), null);
+
+		final ArgumentCaptor<MessageCreator> messageCreatorArgumentCaptor = ArgumentCaptor
+				.forClass(MessageCreator.class);
+
+		verify(jmsTemplate, times(1)).send(anyString(), messageCreatorArgumentCaptor.capture());
+
+		final MessageCreator creator = messageCreatorArgumentCaptor.getValue();
+
+		Assertions.assertThatCode(() -> creator.createMessage(session)).doesNotThrowAnyException();
+	}
+
+}