Ensure star wars example is following best practice

For example, resolveType must not return null.

Author: leebyron

src/__tests__/starWarsData.js

@@ -89,15 +89,7 @@ var droidData = {
  */
 function getCharacter(id) {
   // Returning a promise just to illustrate GraphQL.js's support.
-  return new Promise(resolve => {
-    if (humanData[id] !== undefined) {
-      return resolve(humanData[id]);
-    }
-    if (droidData[id] !== undefined) {
-      return resolve(droidData[id]);
-    }
-    return resolve(null);
-  });
+  return Promise.resolve(humanData[id] || droidData[id]);
 }
 
 /**

src/__tests__/starWarsSchema.js

@@ -127,13 +127,7 @@ var characterInterface = new GraphQLInterfaceType({
     },
   }),
   resolveType: (obj) => {
-    if (starWarsData.Humans[obj.id] !== undefined) {
-      return humanType;
-    }
-    if (starWarsData.Droids[obj.id] !== undefined) {
-      return droidType;
-    }
-    return null;
+    return starWarsData.Humans[obj.id] ? humanType : droidType;
   }
 });