Use putIfAbsent() instead of containsKey

See gh-17913

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/AbstractLoggingSystem.java

@@ -194,12 +194,8 @@ public abstract class AbstractLoggingSystem extends LoggingSystem {
 		}
 
 		public void map(LogLevel system, T nativeLevel) {
-			if (!this.systemToNative.containsKey(system)) {
-				this.systemToNative.put(system, nativeLevel);
-			}
-			if (!this.nativeToSystem.containsKey(nativeLevel)) {
-				this.nativeToSystem.put(nativeLevel, system);
-			}
+			this.systemToNative.putIfAbsent(system, nativeLevel);
+			this.nativeToSystem.putIfAbsent(nativeLevel, system);
 		}
 
 		public LogLevel convertNativeToSystem(T level) {