[JavaScript] Fixed handling of empty arrays/empty strings/booleans/single numbers as valid API responses (#4653) (#4666)

modules/swagger-codegen/src/main/resources/Javascript/ApiClient.mustache

@@ -317,7 +317,7 @@
     // Rely on SuperAgent for parsing response body.
     // See http://visionmedia.github.io/superagent/#parsing-response-bodies
     var data = response.body;
-    if (data == null || !Object.keys(data).length) {
+    if (data == null || (typeof data === 'object' && typeof data.length === 'undefined' && !Object.keys(data).length)) {
       // SuperAgent does not always produce a body; use the unparsed response as a fallback
       data = response.text;
     }

samples/client/petstore/javascript-promise/src/ApiClient.js

@@ -320,7 +320,7 @@
     // Rely on SuperAgent for parsing response body.
     // See http://visionmedia.github.io/superagent/#parsing-response-bodies
     var data = response.body;
-    if (data == null || !Object.keys(data).length) {
+    if (data == null || (typeof data === 'object' && typeof data.length === 'undefined' && !Object.keys(data).length)) {
       // SuperAgent does not always produce a body; use the unparsed response as a fallback
       data = response.text;
     }

samples/client/petstore/javascript/src/ApiClient.js

@@ -320,7 +320,7 @@
     // Rely on SuperAgent for parsing response body.
     // See http://visionmedia.github.io/superagent/#parsing-response-bodies
     var data = response.body;
-    if (data == null || !Object.keys(data).length) {
+    if (data == null || (typeof data === 'object' && typeof data.length === 'undefined' && !Object.keys(data).length)) {
       // SuperAgent does not always produce a body; use the unparsed response as a fallback
       data = response.text;
     }