Use empty string (not null) for release notes body in GitHub release …

…request (fixes ##855)

lib/plugin/github/GitHub.js

@@ -192,7 +192,7 @@ class GitHub extends Release {
     const { version, releaseNotes } = this.getContext();
     const { isPreRelease } = parseVersion(version);
     const name = format(releaseName, this.config.getContext());
-    const body = autoGenerate ? null : releaseNotes;
+    const body = autoGenerate ? '' : releaseNotes || '';
 
     return Object.assign(options, {
       owner,

test/github.js

@@ -15,7 +15,7 @@ const {
 const tokenRef = 'GITHUB_TOKEN';
 const pushRepo = 'git://github.com:user/repo';
 const host = 'github.com';
-const git = { changelog: null };
+const git = { changelog: '' };
 const requestErrorOptions = { request: { url: '', headers: {} }, response: { headers: {} } };
 
 test.serial('should check token and perform checks', async t => {
@@ -89,7 +89,7 @@ test('should create a pre-release and draft release notes', async t => {
 
   interceptAuthentication();
   interceptCollaborator();
-  interceptCreate({ body: { tag_name: '2.0.2', name: 'Release 2.0.2', body: null, prerelease: true, draft: true } });
+  interceptCreate({ body: { tag_name: '2.0.2', name: 'Release 2.0.2', body: '', prerelease: true, draft: true } });
 
   await runTasks(github);
 
@@ -244,7 +244,7 @@ test('should release to alternative host and proxy', async t => {
 test('should release to git.pushRepo', async t => {
   const remote = { api: 'https://my-custom-host.org/api/v3', host: 'my-custom-host.org' };
   interceptCreate(Object.assign({ body: { tag_name: '1.0.1' } }, remote));
-  const options = { git: { pushRepo: 'upstream', changelog: null }, github: { tokenRef, skipChecks: true } };
+  const options = { git: { pushRepo: 'upstream', changelog: '' }, github: { tokenRef, skipChecks: true } };
   const github = factory(GitHub, { options });
   const exec = sinon.stub(github.shell, 'exec').callThrough();
   exec.withArgs('git describe --tags --match=* --abbrev=0').resolves('1.0.0');

test/stub/github.js

@@ -40,7 +40,7 @@ const interceptCreate = ({
   host = 'github.com',
   owner = 'user',
   project = 'repo',
-  body: { tag_name, name = '', body = null, prerelease = false, draft = false, generate_release_notes = false }
+  body: { tag_name, name = '', body = '', prerelease = false, draft = false, generate_release_notes = false }
 } = {}) =>
   nock(api)
     .post(`/repos/${owner}/${project}/releases`, {
@@ -72,7 +72,7 @@ const interceptUpdate = ({
   api = 'https://api.github.com',
   owner = 'user',
   project = 'repo',
-  body: { tag_name, name = '', body = null, prerelease = false, draft = false, generate_release_notes = false }
+  body: { tag_name, name = '', body = '', prerelease = false, draft = false, generate_release_notes = false }
 } = {}) =>
   nock(api)
     .patch(`/repos/${owner}/${project}/releases/1`, { tag_name, name, body, draft, prerelease, generate_release_notes })