Fixed a regression bug with unsubscribing from cancel token; (#4819)

Reverts #4795;

Co-authored-by: Jay <jasonsaayman@gmail.com>

lib/adapters/http.js

@@ -100,7 +100,6 @@ function setProxy(options, configProxy, location) {
 /*eslint consistent-return:0*/
 export default function httpAdapter(config) {
   return new Promise(function dispatchHttpRequest(resolvePromise, rejectPromise) {
-    let onCanceled;
     let data = config.data;
     const responseType = config.responseType;
     const responseEncoding = config.responseEncoding;
@@ -118,11 +117,11 @@ export default function httpAdapter(config) {
       isFinished = true;
 
       if (config.cancelToken) {
-        config.cancelToken.unsubscribe(onCanceled);
+        config.cancelToken.unsubscribe(abort);
       }
 
       if (config.signal) {
-        config.signal.removeEventListener('abort', onCanceled);
+        config.signal.removeEventListener('abort', abort);
       }
 
       emitter.removeAllListeners();

lib/adapters/xhr.js

@@ -232,11 +232,6 @@ export default function xhrAdapter(config) {
       }
     }
 
-    // false, 0 (zero number), and '' (empty string) are valid JSON values
-    if (!requestData && requestData !== false && requestData !== 0 && requestData !== '') {
-      requestData = null;
-    }
-
     const protocol = parseProtocol(fullPath);
 
     if (protocol && platform.protocols.indexOf(protocol) === -1) {
@@ -246,6 +241,6 @@ export default function xhrAdapter(config) {
 
 
     // Send the request
-    request.send(requestData);
+    request.send(requestData || null);
   });
 }