Add starter, make adapter kick in only if needed

spring-shell-jcommander-adapter/pom.xml

@@ -23,6 +23,7 @@
 			<groupId>com.beust</groupId>
 			<artifactId>jcommander</artifactId>
 			<version>1.48</version>
+			<optional>true</optional>
 		</dependency>
 		<dependency>
 			<groupId>org.springframework.boot</groupId>

spring-shell-jcommander-adapter/src/main/java/org/springframework/shell/jcommander/JCommanderParameterResolverAutoConfiguration.java

@@ -16,6 +16,9 @@
 
 package org.springframework.shell.jcommander;
 
+import com.beust.jcommander.JCommander;
+
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Bean;
 
@@ -25,6 +28,7 @@ import org.springframework.context.annotation.Bean;
  * @author Eric Bottard
  */
 @Configuration
+@ConditionalOnClass(JCommander.class)
 public class JCommanderParameterResolverAutoConfiguration {
 
 	@Bean