Update nullability annotations and javadoc.

Reflect allowed null arguments in both documentation as well as supporting annotations.
Going forward we should consider if there is a possibility to restructure Specification and the Predicate handling to avoid this at all (#3521).

See: #3036

spring-data-jpa/src/main/java/org/springframework/data/jpa/domain/Specification.java

@@ -96,12 +96,12 @@ public interface Specification<T> extends Serializable {
 	 * {@link Root} and {@link CriteriaQuery}.
 	 *
 	 * @param root must not be {@literal null}.
-	 * @param query must not be {@literal null}.
+	 * @param query can be {@literal null} to allow overrides that accept {@link jakarta.persistence.criteria.CriteriaDelete} which is an {@link jakarta.persistence.criteria.AbstractQuery} but no {@link CriteriaQuery}.
 	 * @param criteriaBuilder must not be {@literal null}.
 	 * @return a {@link Predicate}, may be {@literal null}.
 	 */
 	@Nullable
-	Predicate toPredicate(Root<T> root, CriteriaQuery<?> query, CriteriaBuilder criteriaBuilder);
+	Predicate toPredicate(Root<T> root, @Nullable CriteriaQuery<?> query, CriteriaBuilder criteriaBuilder);
 
 	/**
 	 * Applies an AND operation to all the given {@link Specification}s.

spring-data-jpa/src/main/java/org/springframework/data/jpa/domain/SpecificationComposition.java

@@ -57,7 +57,7 @@ class SpecificationComposition {
 	}
 
 	@Nullable
-	private static <T> Predicate toPredicate(@Nullable Specification<T> specification, Root<T> root, CriteriaQuery<?> query,
+	private static <T> Predicate toPredicate(@Nullable Specification<T> specification, Root<T> root, @Nullable CriteriaQuery<?> query,
 			CriteriaBuilder builder) {
 		return specification == null ? null : specification.toPredicate(root, query, builder);
 	}

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/JpaSpecificationExecutor.java

@@ -28,6 +28,7 @@ import org.springframework.data.domain.Pageable;
 import org.springframework.data.domain.Sort;
 import org.springframework.data.jpa.domain.Specification;
 import org.springframework.data.repository.query.FluentQuery;
+import org.springframework.lang.Nullable;
 
 /**
  * Interface to allow execution of {@link Specification}s based on the JPA criteria API.
@@ -50,37 +51,45 @@ public interface JpaSpecificationExecutor<T> {
 
 	/**
 	 * Returns all entities matching the given {@link Specification}.
+	 * <p>
+	 * If no {@link Specification} is given all entities matching {@code <T>} will be selected.
 	 *
-	 * @param spec must not be {@literal null}.
+	 * @param spec can be {@literal null}.
 	 * @return never {@literal null}.
 	 */
-	List<T> findAll(Specification<T> spec);
+	List<T> findAll(@Nullable Specification<T> spec);
 
 	/**
 	 * Returns a {@link Page} of entities matching the given {@link Specification}.
+	 * <p>
+	 * If no {@link Specification} is given all entities matching {@code <T>} will be selected.
 	 *
-	 * @param spec must not be {@literal null}.
+	 * @param spec can be {@literal null}.
 	 * @param pageable must not be {@literal null}.
 	 * @return never {@literal null}.
 	 */
-	Page<T> findAll(Specification<T> spec, Pageable pageable);
+	Page<T> findAll(@Nullable Specification<T> spec, Pageable pageable);
 
 	/**
 	 * Returns all entities matching the given {@link Specification} and {@link Sort}.
+	 * <p>
+	 * If no {@link Specification} is given all entities matching {@code <T>} will be selected.
 	 *
-	 * @param spec must not be {@literal null}.
+	 * @param spec can be {@literal null}.
 	 * @param sort must not be {@literal null}.
 	 * @return never {@literal null}.
 	 */
-	List<T> findAll(Specification<T> spec, Sort sort);
+	List<T> findAll(@Nullable Specification<T> spec, Sort sort);
 
 	/**
 	 * Returns the number of instances that the given {@link Specification} will return.
+	 * <p>
+	 * If no {@link Specification} is given all entities matching {@code <T>} will be counted.
 	 *
 	 * @param spec the {@link Specification} to count instances for, must not be {@literal null}.
 	 * @return the number of instances.
 	 */
-	long count(Specification<T> spec);
+	long count(@Nullable Specification<T> spec);
 
 	/**
 	 * Checks whether the data store contains elements that match the given {@link Specification}.
@@ -101,12 +110,14 @@ public interface JpaSpecificationExecutor<T> {
 	 * {@link Specification#toPredicate(Root, CriteriaQuery, CriteriaBuilder)} will be {@literal null} because
 	 * {@link jakarta.persistence.criteria.CriteriaBuilder#createCriteriaDelete(Class)} does not implement
 	 * {@code CriteriaQuery}.
+	 * <p>
+	 * If no {@link Specification} is given all entities matching {@code <T>} will be deleted.
 	 *
-	 * @param spec the {@link Specification} to use for the existence check, must not be {@literal null}.
+	 * @param spec the {@link Specification} to use for the existence check, can not be {@literal null}.
 	 * @return the number of entities deleted.
 	 * @since 3.0
 	 */
-	long delete(Specification<T> spec);
+	long delete(@Nullable Specification<T> spec);
 
 	/**
 	 * Returns entities matching the given {@link Specification} applying the {@code queryFunction} that defines the query

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

@@ -431,7 +431,7 @@ public class SimpleJpaRepository<T, ID> implements JpaRepositoryImplementation<T
 			return new PageImpl<>(findAll());
 		}
 
-		return findAll((root, query, criteriaBuilder) -> null, pageable);
+		return findAll((Specification<T>) null, pageable);
 	}
 
 	@Override
@@ -450,7 +450,7 @@ public class SimpleJpaRepository<T, ID> implements JpaRepositoryImplementation<T
 	}
 
 	@Override
-	public Page<T> findAll(Specification<T> spec, Pageable pageable) {
+	public Page<T> findAll(@Nullable Specification<T> spec, Pageable pageable) {
 
 		TypedQuery<T> query = getQuery(spec, pageable);
 		return pageable.isUnpaged() ? new PageImpl<>(query.getResultList())
@@ -458,7 +458,7 @@ public class SimpleJpaRepository<T, ID> implements JpaRepositoryImplementation<T
 	}
 
 	@Override
-	public List<T> findAll(Specification<T> spec, Sort sort) {
+	public List<T> findAll(@Nullable Specification<T> spec, Sort sort) {
 		return getQuery(spec, sort).getResultList();
 	}
 
@@ -477,7 +477,7 @@ public class SimpleJpaRepository<T, ID> implements JpaRepositoryImplementation<T
 
 	@Override
 	@Transactional
-	public long delete(Specification<T> spec) {
+	public long delete(@Nullable Specification<T> spec) {
 
 		CriteriaBuilder builder = this.entityManager.getCriteriaBuilder();
 		CriteriaDelete<T> delete = builder.createCriteriaDelete(getDomainClass());