[JENKINS-43507] Fix tests with invalid nulls

src/test/java/org/jenkinsci/plugins/github_branch_source/GitHubSCMFileSystemTest.java

@@ -137,7 +137,7 @@ public void prepareMockGitHub() throws Exception {
                get(urlMatching(".*")).atPriority(10).willReturn(aResponse().proxiedFrom("https://api.github.com/")));
        githubRaw.stubFor(get(urlMatching(".*")).atPriority(10)
                .willReturn(aResponse().proxiedFrom("https://raw.githubusercontent.com/")));
        source = new GitHubSCMSource(null, "http://localhost:" + githubApi.port(), null, null, "cloudbeers", "yolo");
        source = new GitHubSCMSource(null, "http://localhost:" + githubApi.port(), GitHubSCMSource.DescriptorImpl.SAME, null, "cloudbeers", "yolo");
    }

    @Test

src/test/java/org/jenkinsci/plugins/github_branch_source/GitHubSCMSourceTest.java

@@ -129,7 +129,7 @@ public void prepareMockGitHub() throws Exception {
                get(urlMatching(".*")).atPriority(10).willReturn(aResponse().proxiedFrom("https://api.github.com/")));
        githubRaw.stubFor(get(urlMatching(".*")).atPriority(10)
                .willReturn(aResponse().proxiedFrom("https://raw.githubusercontent.com/")));
        source = new GitHubSCMSource(null, "http://localhost:" + githubApi.port(), null, null, "cloudbeers", "yolo");
        source = new GitHubSCMSource(null, "http://localhost:" + githubApi.port(), GitHubSCMSource.DescriptorImpl.SAME, null, "cloudbeers", "yolo");
    }

    @Test