CheckAntoraVersionTask has optional properties

buildSrc/src/main/java/org/springframework/gradle/antora/CheckAntoraVersionTask.java

@@ -6,6 +6,7 @@ import org.gradle.api.file.RegularFileProperty;
 import org.gradle.api.provider.Property;
 import org.gradle.api.tasks.Input;
 import org.gradle.api.tasks.InputFile;
+import org.gradle.api.tasks.Optional;
 import org.gradle.api.tasks.TaskAction;
 import org.yaml.snakeyaml.Yaml;
 import org.yaml.snakeyaml.constructor.Constructor;
@@ -54,9 +55,11 @@ public abstract class CheckAntoraVersionTask extends DefaultTask {
 	public abstract Property<String> getAntoraVersion();
 
 	@Input
+	@Optional
 	public abstract Property<String> getAntoraPrerelease();
 
 	@Input
+	@Optional
 	public abstract Property<String> getAntoraDisplayVersion();
 
 	public static class AntoraYml {