Use Map::computeIfAbsent to simplify scope implementations

Closes gh-25038

spring-context/src/main/java/org/springframework/context/support/SimpleThreadScope.java

@@ -67,12 +67,7 @@ public class SimpleThreadScope implements Scope {
 	@Override
 	public Object get(String name, ObjectFactory<?> objectFactory) {
 		Map<String, Object> scope = this.threadScope.get();
-		Object scopedObject = scope.get(name);
+		return scope.computeIfAbsent(name, k -> objectFactory.getObject());
-		if (scopedObject == null) {
-			scopedObject = objectFactory.getObject();
-			scope.put(name, scopedObject);
-		}
-		return scopedObject;
 	}
 
 	@Override

spring-tx/src/main/java/org/springframework/transaction/support/SimpleTransactionScope.java

@@ -50,12 +50,7 @@ public class SimpleTransactionScope implements Scope {
 			TransactionSynchronizationManager.registerSynchronization(new CleanupSynchronization(scopedObjects));
 			TransactionSynchronizationManager.bindResource(this, scopedObjects);
 		}
-		Object scopedObject = scopedObjects.scopedInstances.get(name);
+		return scopedObjects.scopedInstances.computeIfAbsent(name, k -> objectFactory.getObject());
-		if (scopedObject == null) {
-			scopedObject = objectFactory.getObject();
-			scopedObjects.scopedInstances.put(name, scopedObject);
-		}
-		return scopedObject;
 	}
 
 	@Override