Fix version command attributes

- Now passing version command attributes
  even if those are nulls(not set) as ST
  logs those in a listener as errors while
  it doesn't cause any failures.
- Change all LoggingSTErrorListener methods
  into debug level to limit more noise.
- Fixes #363

spring-shell-core/src/main/java/org/springframework/shell/style/TemplateExecutor.java

@@ -94,22 +94,22 @@ public class TemplateExecutor {
 
 		@Override
 		public void compileTimeError(STMessage msg) {
-			log.error("compileTimeError [{}]", msg);
+			log.debug("compileTimeError [{}]", msg);
 		}
 
 		@Override
 		public void runTimeError(STMessage msg) {
-			log.error("runTimeError [{}]", msg);
+			log.debug("runTimeError [{}]", msg);
 		}
 
 		@Override
 		public void IOError(STMessage msg) {
-			log.error("IOError [{}]", msg);
+			log.debug("IOError [{}]", msg);
 		}
 
 		@Override
 		public void internalError(STMessage msg) {
-			log.error("internalError [{}]", msg);
+			log.debug("internalError [{}]", msg);
 		}
 	}
 }