Update documentation for repository Pageable and Sort arguments.

Replace outdated `null` acceptance for `Pageable` with `Pageable.unpaged()`
 `QueryByExampleExecutor#findAll(Example<S> example, Pageable pageable)` should does not accept null values since there is `Pageable.unpaged()`. Furthermore, the same applies to `PagingAndSortingRepository#findAll(Pageable pageable)`.

Related ticket: spring-projects/spring-data-jpa/issues/2464
Closes #2574

src/main/java/org/springframework/data/repository/PagingAndSortingRepository.java

@@ -45,7 +45,7 @@ public interface PagingAndSortingRepository<T, ID> extends Repository<T, ID> {
 	/**
 	 * Returns a {@link Page} of entities meeting the paging restriction provided in the {@code Pageable} object.
 	 *
-	 * @param pageable
+	 * @param pageable must not be {@literal null}.
 	 * @return a page of entities
 	 */
 	Page<T> findAll(Pageable pageable);

src/main/java/org/springframework/data/repository/query/QueryByExampleExecutor.java

@@ -29,6 +29,7 @@ import org.springframework.data.domain.Sort;
  * @param <T>
  * @author Mark Paluch
  * @author Christoph Strobl
+ * @author Diego Krupitza
  * @since 1.12
  * @see ListQueryByExampleExecutor
  */
@@ -68,7 +69,7 @@ public interface QueryByExampleExecutor<T> {
 	 * {@link Page} is returned.
 	 *
 	 * @param example must not be {@literal null}.
-	 * @param pageable can be {@literal null}.
+	 * @param pageable must not be {@literal null}.
 	 * @return a {@link Page} of entities matching the given {@link Example}.
 	 */
 	<S extends T> Page<S> findAll(Example<S> example, Pageable pageable);