TaskValidation now handles invalid task definition name

resolves #3363

Author: cppwfs

spring-cloud-dataflow-server-core/src/main/java/org/springframework/cloud/dataflow/server/service/impl/validation/DefaultTaskValidationService.java

@@ -21,6 +21,7 @@
 import org.springframework.cloud.dataflow.core.dsl.TaskParser;
 import org.springframework.cloud.dataflow.registry.service.AppRegistryService;
 import org.springframework.cloud.dataflow.server.DockerValidatorProperties;
+import org.springframework.cloud.dataflow.server.repository.NoSuchTaskDefinitionException;
 import org.springframework.cloud.dataflow.server.repository.TaskDefinitionRepository;
 import org.springframework.cloud.dataflow.server.service.TaskValidationService;
 import org.springframework.cloud.dataflow.server.service.ValidationStatus;
@@ -60,6 +61,9 @@ public DefaultTaskValidationService(AppRegistryService appRegistry,
 	public ValidationStatus validateTask(String name) {
 		validateTaskName(name);
 		TaskDefinition definition = this.taskDefinitionRepository.findByTaskName(name);
+		if(definition == null) {
+			throw new NoSuchTaskDefinitionException(name);
+		}
 		ValidationStatus validationStatus = new ValidationStatus(
 				definition.getName(),
 				definition.getDslText());

spring-cloud-dataflow-server-core/src/test/java/org/springframework/cloud/dataflow/server/service/impl/DefaultTaskExecutionServiceTests.java

@@ -365,6 +365,14 @@ public void validateValidTaskTest() {
 			assertEquals("valid", validationStatus.getAppsStatuses().get("task:simpleTask"));
 		}
 
+		@Test(expected = NoSuchTaskDefinitionException.class)
+		@DirtiesContext
+		public void validateMissingTaskDefinitionTest() {
+			initializeSuccessfulRegistry(appRegistry);
+			ValidationStatus validationStatus = taskValidationService.validateTask("simpleTask");
+			assertEquals("valid", validationStatus.getAppsStatuses().get("task:simpleTask"));
+		}
+
 		@Test
 		@DirtiesContext
 		public void validateInvalidTaskTest() {