Remove concatenations with empty string

Closes gh-10512

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/trace/WebRequestTraceFilter.java

@@ -214,7 +214,7 @@ public class WebRequestTraceFilter extends OncePerRequestFilter implements Order
 	private void addTimeTaken(Map<String, Object> trace, long startTime) {
 		long timeTaken = System.nanoTime() - startTime;
 		add(trace, Include.TIME_TAKEN, "timeTaken",
-				"" + TimeUnit.NANOSECONDS.toMillis(timeTaken));
+				String.valueOf(TimeUnit.NANOSECONDS.toMillis(timeTaken)));
 	}
 
 	@SuppressWarnings("unchecked")

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/main/java/org/springframework/boot/maven/StopMojo.java

@@ -128,7 +128,7 @@ public class StopMojo extends AbstractMojo {
 		}
 		catch (InstanceNotFoundException ex) {
 			throw new MojoExecutionException(
-					"Spring application lifecycle JMX bean not found (fork is " + ""
+					"Spring application lifecycle JMX bean not found (fork is "
 							+ this.fork + "). Could not stop application gracefully",
 					ex);
 		}