Throw a more informative exception if function does not exist

Fixes gh-36

src/main/java/io/projectriff/invoker/ApplicationRunner.java

@@ -90,7 +90,12 @@ public Object getBean(String name) {
 			if (containsBeanByName(name)) {
 				return getBeanByName(name);
 			}
-			return getBeanByType(name);
+			try {
+				return getBeanByType(name);
+			}
+			catch (Exception e) {
+				// not there
+			}
 		}
 		return null;
 	}

src/main/java/io/projectriff/invoker/GrpcConfiguration.java

@@ -75,6 +75,10 @@ public void start() throws IOException {
 		try {
 			Function<Flux<?>, Flux<?>> function = catalog.lookup(Function.class,
 					functions.getFunctionName());
+			if (function == null) {
+				throw new IllegalStateException(
+						"No such function: " + functions.getFunctionName());
+			}
 			this.server = ServerBuilder.forPort(this.port)
 					.addService(new JavaFunctionInvokerServer(function, this.mapper,
 							inspector.getInputType(function),

src/test/java/io/projectriff/invoker/ExceptionConverterTests.java

@@ -113,6 +113,7 @@ private void checkStatus(Throwable cause, Status.Code expectedCode) {
 		assertThat(s.getCause()).isEqualTo(cause);
 	}
 
+	@SuppressWarnings("serial")
 	private static class TestException extends Throwable {
 		TestException(String message) {
 			super(message);

src/test/java/io/projectriff/invoker/GrpcIsolatedTests.java

@@ -67,6 +67,14 @@ public void fluxFunctionNotIsolated() throws Exception {
 						+ "?handler=io.projectriff.functions.FluxDoubler");
 	}
 
+	@Test
+	public void nonExistentFunction() throws Exception {
+		expected.expect(BeanCreationException.class);
+		SpringApplication.run(JavaFunctionInvokerApplication.class, "--server.port=0",
+				"--grpc.port=" + port, "--function.uri=file:target/test-classes"
+						+ "?handler=io.projectriff.functions.NotHere");
+	}
+
 	@Test
 	public void fluxFunction() throws Exception {
 		runner.run("--server.port=0", "--grpc.port=" + port,
@@ -151,6 +159,13 @@ public void appClassPath() throws Exception {
 		assertThat(result).contains("10");
 	}
 
+	@Test(expected = IllegalStateException.class)
+	public void nonExistentFunctionWithMain() throws Exception {
+		runner.run("--server.port=0", "--grpc.port=" + port,
+				"--function.uri=app:classpath?" + "handler=notThere&"
+						+ "main=io.projectriff.functions.FunctionApp");
+	}
+
 	@Test
 	public void mainClassBeanName() throws Exception {
 		runner.run("--server.port=0", "--grpc.port=" + port,