Handle empty response

addon/mixins/adapter-fetch.js

@@ -130,7 +130,9 @@ export default Ember.Mixin.create({
       })
       .then((response) => {
         if (response.ok) {
-          const bodyPromise = response.json();
+          // We want to check that there is a body in the response, otherwise JSON.parse will throw an error.
+          // Instead, we'll let Ember Data handle an empty response.
+          const bodyPromise = response.headers.get('content-length') ? response.json() : {};
           return this.ajaxSuccess(response, bodyPromise, requestData);
         }
         throw this.ajaxError(null, response, requestData);