fix(serverless): gracefully fail with 400 for null body (#38)

index.js

@@ -57,6 +57,14 @@ module.exports.serverless = appFn => {
     // Convert the payload to an Object if API Gateway stringifies it
     event.body = (typeof event.body === 'string') ? JSON.parse(event.body) : event.body
 
+    // Bail for null body
+    if (!event.body) {
+      return context.done(null, {
+        statusCode: 400,
+        body: 'Event body is null.'
+      })
+    }
+
     // Do the thing
     console.log(`Received event ${e}${event.body.action ? ('.' + event.body.action) : ''}`)
     if (event) {

tests/index.test.js

@@ -34,4 +34,20 @@ describe('serverless-lambda', () => {
     expect(context.done).toHaveBeenCalled()
     expect(spy).toHaveBeenCalled()
   })
+
+  it('responds with a 400 error when body is null', async () => {
+    const event = {
+      body: null,
+      headers: {
+        'X-Github-Event': 'issues',
+        'x-github-delivery': 123
+      }
+    }
+
+    await handler(event, context)
+    expect(context.done).toHaveBeenCalledWith(null, expect.objectContaining({
+      statusCode: 400
+    }))
+    expect(spy).not.toHaveBeenCalled()
+  })
 })