fix(headers): fixed common Content-Type header merging;

lib/defaults/index.js

@@ -8,10 +8,6 @@ import toURLEncodedForm from '../helpers/toURLEncodedForm.js';
 import platform from '../platform/index.js';
 import formDataToJSON from '../helpers/formDataToJSON.js';
 
-const DEFAULT_CONTENT_TYPE = {
-  'Content-Type': undefined
-};
-
 /**
  * It takes a string, tries to parse it, and if it fails, it returns the stringified version
  * of the input
@@ -155,12 +151,8 @@ const defaults = {
   }
 };
 
-utils.forEach(['delete', 'get', 'head'], function forEachMethodNoData(method) {
+utils.forEach(['delete', 'get', 'head', 'post', 'put', 'patch'], (method) => {
   defaults.headers[method] = {};
 });
 
-utils.forEach(['post', 'put', 'patch'], function forEachMethodWithData(method) {
-  defaults.headers[method] = utils.merge(DEFAULT_CONTENT_TYPE);
-});
-
 export default defaults;

test/specs/headers.spec.js

@@ -1,3 +1,5 @@
+import assert from "assert";
+
 const {AxiosHeaders} = axios;
 
 function testHeaderValue(headers, key, val) {
@@ -44,6 +46,26 @@ describe('headers', function () {
     });
   });
 
+  it('should respect common Content-Type header', function () {
+    const instance = axios.create();
+
+    instance.defaults.headers.common['Content-Type'] = 'application/custom';
+
+    instance.patch('/foo', "");
+
+    const expectedHeaders = {
+      'Content-Type': "application/custom"
+    };
+
+    return getAjaxRequest().then(function (request) {
+      for (const key in expectedHeaders) {
+        if (expectedHeaders.hasOwnProperty(key)) {
+          expect(request.requestHeaders[key]).toEqual(expectedHeaders[key]);
+        }
+      }
+    });
+  });
+
   it('should add extra headers for post', function (done) {
     const headers = axios.defaults.headers.common;