fix: can't delete GitHub Enterprise servers

src/main/java/org/jenkinsci/plugins/github_branch_source/GitHubConfiguration.java

@@ -59,6 +59,7 @@ public GitHubConfiguration() {
 
     @Override
     public boolean configure(StaplerRequest req, JSONObject json) throws FormException {
+        setEndpoints(null);
         req.bindJSON(this, json);
         return true;
     }

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

@@ -0,0 +1,66 @@
+package org.jenkinsci.plugins.github_branch_source;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.hasSize;
+import static org.hamcrest.Matchers.is;
+
+import java.util.List;
+import org.htmlunit.html.HtmlForm;
+import org.htmlunit.html.HtmlInput;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.jvnet.hudson.test.JenkinsRule;
+
+public class GitHubConfigurationTest {
+
+    @Rule
+    public final JenkinsRule j = new JenkinsRule();
+
+    private GitHubConfiguration globalConfig;
+
+    @Before
+    public void setUp() {
+        globalConfig = GitHubConfiguration.all().getInstance(GitHubConfiguration.class);
+    }
+
+    @Test
+    public void configRoundTripTestNoChanges() throws Exception {
+        globalConfig.addEndpoint(new Endpoint("https://www.example.com/api/v3", "example.com"));
+        List<Endpoint> endpoints = globalConfig.getEndpoints();
+        assertThat(endpoints, is(hasSize(1)));
+        Endpoint endpoint = endpoints.get(0);
+        assertThat(endpoint.getApiUri(), is("https://www.example.com/api/v3"));
+        assertThat(endpoint.getName(), is("example.com"));
+
+        // Submit the global configuration page with no changes
+        j.configRoundtrip();
+
+        endpoints = globalConfig.getEndpoints();
+        assertThat(endpoints, is(hasSize(1)));
+        endpoint = endpoints.get(0);
+        assertThat(endpoint.getApiUri(), is("https://www.example.com/api/v3"));
+        assertThat(endpoint.getName(), is("example.com"));
+    }
+
+    @Test
+    public void configDeleteEndpoint() throws Exception {
+        globalConfig.addEndpoint(new Endpoint("https://www.example.com/api/v3", "example.com"));
+        List<Endpoint> endpoints = globalConfig.getEndpoints();
+        assertThat(endpoints, is(hasSize(1)));
+
+        j.configRoundtrip();
+
+        // delete the endpoint in the UI
+        HtmlForm config = j.createWebClient().goTo("configure").getFormByName("config");
+        HtmlInput input = config.getInputByName("_.apiUri");
+        input.getParentNode().removeChild(input);
+        input = config.getInputByName("_.name");
+        input.getParentNode().removeChild(input);
+        j.submit(config);
+
+        // there should be no endpoints now
+        endpoints = globalConfig.getEndpoints();
+        assertThat(endpoints, is(hasSize(0)));
+    }
+}