Merge pull request #260 from jglick/null-launcher

Do not pass a null `Launcher` to `DockerClient`

Author: jglick

src/main/java/org/jenkinsci/plugins/docker/workflow/WithContainerStep.java

@@ -107,7 +107,7 @@ public String getToolName() {
         this.toolName = Util.fixEmpty(toolName);
     }
 
-    private static void destroy(String container, Launcher launcher, Node node, EnvVars launcherEnv, String toolName) throws Exception {
+    private static void destroy(String container, @NonNull Launcher launcher, Node node, EnvVars launcherEnv, String toolName) throws Exception {
         new DockerClient(launcher, node, toolName).stop(launcherEnv, container);
     }
 
@@ -410,7 +410,10 @@ private static class Callback extends BodyExecutionCallback.TailCall {
         }
 
         @Override protected void finished(StepContext context) throws Exception {
-            destroy(container, context.get(Launcher.class), context.get(Node.class), context.get(EnvVars.class), toolName);
+            Launcher launcher = context.get(Launcher.class);
+            if (launcher != null) {
+                destroy(container, launcher, context.get(Node.class), context.get(EnvVars.class), toolName);
+            }
         }
 
     }