Support plain boolean without option annotations

- Fix so that we can have `boolean arg` without using
  `@Option` or `@ShellOption` defaulting to false.
- Fixes #744

spring-shell-core/src/main/java/org/springframework/shell/command/annotation/support/CommandRegistrationFactoryBean.java

@@ -331,6 +331,8 @@ class CommandRegistrationFactoryBean implements FactoryBean<CommandRegistration>
 				optionSpec.position(mp.getParameterIndex());
 				if (ClassUtils.isAssignable(boolean.class, parameterType)) {
 					optionSpec.arity(OptionArity.ZERO_OR_ONE);
+					optionSpec.required(false);
+					optionSpec.defaultValue("false");
 				}
 				else if (ClassUtils.isAssignable(Boolean.class, parameterType)) {
 					optionSpec.arity(OptionArity.ZERO_OR_ONE);