Make credentials-binding dep optional (#3971)

Author: jglick

pom.xml

@@ -132,6 +132,7 @@
     <dependency>
       <groupId>org.jenkins-ci.plugins</groupId>
       <artifactId>credentials-binding</artifactId>
+      <optional>true</optional>
     </dependency>
     <dependency>
       <groupId>org.jenkins-ci.plugins</groupId>

src/main/java/jenkins/plugins/git/GitUsernamePasswordBinding.java

@@ -9,7 +9,6 @@
 import hudson.Launcher;
 import hudson.model.Run;
 import hudson.model.TaskListener;
-import hudson.Extension;
 import hudson.plugins.git.GitSCM;
 import hudson.plugins.git.GitTool;
 import hudson.util.ListBoxModel;
@@ -23,6 +22,7 @@
 import org.jenkinsci.plugins.gitclient.CliGitAPIImpl;
 import org.jenkinsci.plugins.gitclient.Git;
 import org.jenkinsci.plugins.gitclient.GitClient;
+import org.jenkinsci.plugins.variant.OptionalExtension;
 import org.kohsuke.stapler.DataBoundConstructor;
 
 import java.io.IOException;
@@ -200,7 +200,7 @@ private String windowsArgEncodeFileName(String filename) {
 
     // Mistakenly defined GitUsernamePassword in first release, prefer gitUsernamePassword as symbol
     @Symbol({"gitUsernamePassword", "GitUsernamePassword"})
-    @Extension
+    @OptionalExtension(requirePlugins = "credentials-binding")
     public static final class DescriptorImpl extends BindingDescriptor<StandardUsernamePasswordCredentials> {
 
         @NonNull