GH-1077 Update AWSLambdaUtils.java with null check

Resolves #1077 by checking for a null package, which can happen when the inputType is a Message that encloses a primitive generic type

Update AWSTypesMessageConverter.java

Added additional fixes for #1077 in AWTypesMessageConverter

Update FunctionInvokerTests.java

Added unit tests to verify fix for #1077

Checkstyle fix

Resolves #1078

spring-cloud-function-adapters/spring-cloud-function-adapter-aws/src/test/java/org/springframework/cloud/function/adapter/aws/FunctionInvokerTests.java

@@ -1407,6 +1407,21 @@ public class FunctionInvokerTests {
 		assertThat(result.get("body")).isEqualTo("\"olleh\"");
 	}
 
+	@Test
+	public void testPrimitiveMessage() throws Exception {
+		System.setProperty("MAIN_CLASS", PrimitiveConfiguration.class.getName());
+		System.setProperty("spring.cloud.function.definition", "returnByteArrayAsMessage");
+		FunctionInvoker invoker = new FunctionInvoker();
+
+		String testString = "{ \"message\": \"Hello, world!\" }";
+		InputStream targetStream = new ByteArrayInputStream(testString.getBytes());
+		ByteArrayOutputStream output = new ByteArrayOutputStream();
+		invoker.handleRequest(targetStream, output, null);
+
+		String result = output.toString();
+		assertThat(result).isEqualTo(testString);
+	}
+
 	@EnableAutoConfiguration
 	@Configuration
 	public static class AuthorizerConfiguration {
@@ -1811,6 +1826,17 @@ public class FunctionInvokerTests {
 		}
 	}
 
+	@EnableAutoConfiguration
+	@Configuration
+	public static class PrimitiveConfiguration {
+		@Bean
+		public Function<Message<byte[]>, byte[]> returnByteArrayAsMessage() {
+			return v -> {
+				return v.getPayload();
+			};
+		}
+	}
+
 	public static class Person {
 		private String name;