Fix getServiceEndpoint

Author: rddimon

src/globals.ts

@@ -70,7 +70,7 @@ export default class Globals {
     public static getServiceEndpoint (service: string) {
       if (Globals.serverless.providers.aws.sdk) {
         const serviceConf = Globals.serverless.providers.aws.sdk.config[service];
-        return serviceConf.endpoint || null;
+        return (serviceConf && serviceConf.endpoint) || null;
       }
       return null;
     }