fix(stepfunctions): make Fail.error optional (#2042)

Error codes are optional in ASL.

Author: spg

packages/@aws-cdk/aws-stepfunctions/lib/states/fail.ts

@@ -15,8 +15,10 @@ export interface FailProps {
 
     /**
      * Error code used to represent this failure
+     *
+     * @default No error code
      */
-    error: string;
+    error?: string;
 
     /**
      * A description for the cause of the failure
@@ -34,10 +36,10 @@ export interface FailProps {
 export class Fail extends State {
     public readonly endStates: INextable[] = [];
 
-    private readonly error: string;
+    private readonly error?: string;
     private readonly cause?: string;
 
-    constructor(scope: cdk.Construct, id: string, props: FailProps) {
+    constructor(scope: cdk.Construct, id: string, props: FailProps = {}) {
         super(scope, id, props);
 
         this.error = props.error;
@@ -55,4 +57,4 @@ export class Fail extends State {
             Cause: this.cause,
         };
     }
-}
+}

packages/@aws-cdk/aws-stepfunctions/test/test.fail.ts

@@ -0,0 +1,13 @@
+import cdk = require('@aws-cdk/cdk');
+import { Test } from 'nodeunit';
+import stepfunctions = require('../lib');
+
+export = {
+    'Props are optional'(test: Test) {
+        const stack = new cdk.Stack();
+
+        new stepfunctions.Fail(stack, 'Fail');
+
+        test.done();
+    }
+};