Nullability refinements on private and static methods

Based on IntelliJ IDEA 2017.3 introspection results.

Issue: SPR-15756

spring-tx/src/main/java/org/springframework/transaction/interceptor/TransactionAspectSupport.java

@@ -448,7 +448,6 @@ public abstract class TransactionAspectSupport implements BeanFactoryAware, Init
 		if (txAttr != null && txAttr.getName() == null) {
 			txAttr = new DelegatingTransactionAttribute(txAttr) {
 				@Override
-				@Nullable
 				public String getName() {
 					return joinpointIdentification;
 				}