Polishing.

Revise nullability requirements around non-nullable specifications.

Original Pull Request: #3578

Author: mp911de

Diff for: spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/support/SimpleJpaRepository.java

@@ -720,7 +720,9 @@ protected Page<T> readPage(TypedQuery<T> query, Pageable pageable, Specification
 	 */
 	@Contract("_, _, _, null -> fail")
 	protected <S extends T> Page<S> readPage(TypedQuery<S> query, Class<S> domainClass, Pageable pageable,
-			@Nullable Specification<S> spec) {
+			Specification<S> spec) {
+
+		Assert.notNull(spec, "Specification must not be null");
 
 		Assert.notNull(spec, "Specification must not be null");
 
@@ -739,7 +741,7 @@ protected <S extends T> Page<S> readPage(TypedQuery<S> query, Class<S> domainCla
 	 * @param spec must not be {@literal null}.
 	 * @param pageable must not be {@literal null}.
 	 */
-	protected TypedQuery<T> getQuery(@Nullable Specification<T> spec, Pageable pageable) {
+	protected TypedQuery<T> getQuery(Specification<T> spec, Pageable pageable) {
 		return getQuery(spec, getDomainClass(), pageable.getSort());
 	}