Remove unnecessary @Nullable annotations

* `DefaultPersistenceUnitManager.java`
`dataSourceLookup` is initialized with a non-null `DataSourceLookup`, so `getDataSourceLookup()` does not return `null`.

* `TestContextTransactionUtils.java`
The transaction attribute name is stored as a non-null value, so `getName()` does not return `null`.

* `RequestContext.java`
The model is represented by a `Map` rather than a nullable value, so `getModel()` can return a non-null `Map`.

Closes gh-37379

Signed-off-by: Tran Ngoc Nhan <ngocnhan.tran1996@gmail.com>

spring-orm/src/main/java/org/springframework/orm/jpa/persistenceunit/DefaultPersistenceUnitManager.java

@@ -344,7 +344,7 @@ public class DefaultPersistenceUnitManager
 	 * persistence provider, resolving data source names in {@code persistence.xml}
 	 * against Spring-managed DataSource instances.
 	 */
-	public @Nullable DataSourceLookup getDataSourceLookup() {
+	public DataSourceLookup getDataSourceLookup() {
 		return this.dataSourceLookup;
 	}
 

spring-test/src/main/java/org/springframework/test/context/transaction/TestContextTransactionUtils.java

@@ -275,7 +275,7 @@ public abstract class TestContextTransactionUtils {
 		}
 
 		@Override
-		public @Nullable String getName() {
+		public String getName() {
 			return this.name;
 		}
 	}

spring-webflux/src/main/java/org/springframework/web/reactive/result/view/RequestContext.java

@@ -112,9 +112,9 @@ public class RequestContext {
 
 	/**
 	 * Return the model Map that this RequestContext encapsulates, if any.
-	 * @return the populated model Map, or {@code null} if none available
+	 * @return the populated model Map
 	 */
-	public @Nullable Map<String, Object> getModel() {
+	public Map<String, Object> getModel() {
 		return this.model;
 	}