Fix issue #506.

Author: nedtwigg

plugin-gradle/src/main/java/com/diffplug/gradle/spotless/SpotlessExtension.java

@@ -59,12 +59,13 @@ public SpotlessExtension(Project project) {
 		rootApplyTask = project.task(EXTENSION + APPLY);
 		rootApplyTask.setGroup(TASK_GROUP);
 		rootApplyTask.setDescription(APPLY_DESCRIPTION);
-		if (project.getRootProject() == project) {
-			registerDependenciesTask = project.getTasks().create(RegisterDependenciesTask.TASK_NAME, RegisterDependenciesTask.class);
+
+		RegisterDependenciesTask registerDependenciesTask = (RegisterDependenciesTask) project.getRootProject().getTasks().findByName(RegisterDependenciesTask.TASK_NAME);
+		if (registerDependenciesTask == null) {
+			registerDependenciesTask = project.getRootProject().getTasks().create(RegisterDependenciesTask.TASK_NAME, RegisterDependenciesTask.class);
 			registerDependenciesTask.setup();
-		} else {
-			registerDependenciesTask = project.getRootProject().getPlugins().apply(SpotlessPlugin.class).spotlessExtension.registerDependenciesTask;
 		}
+		this.registerDependenciesTask = registerDependenciesTask;
 	}
 
 	/** Line endings (if any). */

plugin-gradle/src/test/java/com/diffplug/gradle/spotless/MultiProjectAfterEvaluate.java

@@ -35,7 +35,7 @@ public void failureDoesntTriggerAll() throws IOException {
 						"}",
 						"spotless { java { googleJavaFormat() } }");
 		String output = gradleRunner6().withArguments("spotlessApply", "--warning-mode", "all").build().getOutput().replace("\r\n", "\n");
-		Assertions.assertThat(output).contains("Using method Project#afterEvaluate(Action) when the project is already evaluated has been deprecated.");
+		Assertions.assertThat(output).doesNotContain("Using method Project#afterEvaluate(Action) when the project is already evaluated has been deprecated.");
 	}
 
 	private final GradleRunner gradleRunner6() throws IOException {