diff --git a/spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/JpaSpecificationExecutor.java b/spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/JpaSpecificationExecutor.java
index e7529f6e2..7f59d83bb 100644
--- a/spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/JpaSpecificationExecutor.java
+++ b/spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/JpaSpecificationExecutor.java
@@ -24,7 +24,6 @@ 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.
@@ -32,65 +31,66 @@ import org.springframework.lang.Nullable;
  * @author Oliver Gierke
  * @author Christoph Strobl
  * @author Diego Krupitza
+ * @author Mark Paluch
  */
 public interface JpaSpecificationExecutor<T> {
 
 	/**
 	 * Returns a single entity matching the given {@link Specification} or {@link Optional#empty()} if none found.
 	 *
-	 * @param spec can be {@literal null}.
+	 * @param spec must not be {@literal null}.
 	 * @return never {@literal null}.
 	 * @throws org.springframework.dao.IncorrectResultSizeDataAccessException if more than one entity found.
 	 */
-	Optional<T> findOne(@Nullable Specification<T> spec);
+	Optional<T> findOne(Specification<T> spec);
 
 	/**
 	 * Returns all entities matching the given {@link Specification}.
 	 *
-	 * @param spec can be {@literal null}.
+	 * @param spec must not be {@literal null}.
 	 * @return never {@literal null}.
 	 */
-	List<T> findAll(@Nullable Specification<T> spec);
+	List<T> findAll(Specification<T> spec);
 
 	/**
 	 * Returns a {@link Page} of entities matching the given {@link Specification}.
 	 *
-	 * @param spec can be {@literal null}.
+	 * @param spec must not be {@literal null}.
 	 * @param pageable must not be {@literal null}.
 	 * @return never {@literal null}.
 	 */
-	Page<T> findAll(@Nullable Specification<T> spec, Pageable pageable);
+	Page<T> findAll(Specification<T> spec, Pageable pageable);
 
 	/**
 	 * Returns all entities matching the given {@link Specification} and {@link Sort}.
 	 *
-	 * @param spec can be {@literal null}.
+	 * @param spec must not be {@literal null}.
 	 * @param sort must not be {@literal null}.
 	 * @return never {@literal null}.
 	 */
-	List<T> findAll(@Nullable Specification<T> spec, Sort sort);
+	List<T> findAll(Specification<T> spec, Sort sort);
 
 	/**
 	 * Returns the number of instances that the given {@link Specification} will return.
 	 *
-	 * @param spec the {@link Specification} to count instances for. Can be {@literal null}.
+	 * @param spec the {@link Specification} to count instances for, must not be {@literal null}.
 	 * @return the number of instances.
 	 */
-	long count(@Nullable Specification<T> spec);
+	long count(Specification<T> spec);
 
 	/**
 	 * Checks whether the data store contains elements that match the given {@link Specification}.
-	 * 
-	 * @param spec the {@link Specification} to use for the existence check. Must not be {@literal null}.
-	 * @return <code>true</code> if the data store contains elements that match the given {@link Specification} otherwise
-	 *         <code>false</code>.
+	 *
+	 * @param spec the {@link Specification} to use for the existence check, ust not be {@literal null}.
+	 * @return {@code true} if the data store contains elements that match the given {@link Specification} otherwise
+	 *         {@code false}.
 	 */
 	boolean exists(Specification<T> spec);
 
 	/**
 	 * Deletes by the {@link Specification} and returns the number of rows 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, must not be {@literal null}.
 	 * @return the number of entities deleted
 	 */
 	long delete(Specification<T> spec);
@@ -99,8 +99,8 @@ public interface JpaSpecificationExecutor<T> {
 	 * Returns entities matching the given {@link Specification} applying the {@code queryFunction} that defines the query
 	 * and its result type.
 	 *
-	 * @param spec – must not be null.
-	 * @param queryFunction – the query function defining projection, sorting, and the result type
+	 * @param spec must not be null.
+	 * @param queryFunction the query function defining projection, sorting, and the result type
 	 * @return all entities matching the given Example.
 	 * @since 3.0
 	 */
diff --git a/spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/support/SimpleJpaRepository.java b/spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/support/SimpleJpaRepository.java
index 38ea619fa..d83d5f50f 100644
--- a/spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/support/SimpleJpaRepository.java
+++ b/spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/support/SimpleJpaRepository.java
@@ -447,7 +447,7 @@ public class SimpleJpaRepository<T, ID> implements JpaRepositoryImplementation<T
 	}
 
 	@Override
-	public Optional<T> findOne(@Nullable Specification<T> spec) {
+	public Optional<T> findOne(Specification<T> spec) {
 
 		try {
 			return Optional.of(getQuery(spec, Sort.unsorted()).setMaxResults(2).getSingleResult());
@@ -457,12 +457,12 @@ public class SimpleJpaRepository<T, ID> implements JpaRepositoryImplementation<T
 	}
 
 	@Override
-	public List<T> findAll(@Nullable Specification<T> spec) {
+	public List<T> findAll(Specification<T> spec) {
 		return getQuery(spec, Sort.unsorted()).getResultList();
 	}
 
 	@Override
-	public Page<T> findAll(@Nullable Specification<T> spec, Pageable pageable) {
+	public Page<T> findAll(Specification<T> spec, Pageable pageable) {
 
 		TypedQuery<T> query = getQuery(spec, pageable);
 		return isUnpaged(pageable) ? new PageImpl<>(query.getResultList())
@@ -470,10 +470,51 @@ public class SimpleJpaRepository<T, ID> implements JpaRepositoryImplementation<T
 	}
 
 	@Override
-	public List<T> findAll(@Nullable Specification<T> spec, Sort sort) {
+	public List<T> findAll(Specification<T> spec, Sort sort) {
 		return getQuery(spec, sort).getResultList();
 	}
 
+	@Override
+	public boolean exists(Specification<T> spec) {
+
+		CriteriaQuery<Integer> cq = this.em.getCriteriaBuilder().createQuery(Integer.class);
+		cq.select(this.em.getCriteriaBuilder().literal(1));
+		applySpecificationToCriteria(spec, getDomainClass(), cq);
+		TypedQuery<Integer> query = applyRepositoryMethodMetadata(this.em.createQuery(cq));
+		return query.setMaxResults(1).getResultList().size() == 1;
+	}
+
+	@Override
+	public long delete(Specification<T> spec) {
+
+		CriteriaBuilder builder = this.em.getCriteriaBuilder();
+		CriteriaDelete<T> delete = builder.createCriteriaDelete(getDomainClass());
+
+		if (spec != null) {
+			Predicate predicate = spec.toPredicate(delete.from(getDomainClass()), null, builder);
+
+			if (predicate != null) {
+				delete.where(predicate);
+			}
+		}
+
+		return this.em.createQuery(delete).executeUpdate();
+	}
+
+	@Override
+	public <S extends T, R> R findBy(Specification<T> spec, Function<FetchableFluentQuery<S>, R> queryFunction) {
+
+		Assert.notNull(spec, "Specification must not be null");
+		Assert.notNull(queryFunction, "Query function must not be null");
+
+		Function<Sort, TypedQuery<T>> finder = sort -> getQuery(spec, getDomainClass(), sort);
+
+		FetchableFluentQuery<R> fluentQuery = new FetchableFluentQueryBySpecification<T, R>(spec, getDomainClass(),
+				Sort.unsorted(), null, finder, this::count, this::exists, this.em);
+
+		return queryFunction.apply((FetchableFluentQuery<S>) fluentQuery);
+	}
+
 	@Override
 	public <S extends T> Optional<S> findOne(Example<S> example) {
 
@@ -503,32 +544,6 @@ public class SimpleJpaRepository<T, ID> implements JpaRepositoryImplementation<T
 		return query.setMaxResults(1).getResultList().size() == 1;
 	}
 
-	@Override
-	public boolean exists(Specification<T> spec) {
-
-		CriteriaQuery<Integer> cq = this.em.getCriteriaBuilder().createQuery(Integer.class);
-		cq.select(this.em.getCriteriaBuilder().literal(1));
-		applySpecificationToCriteria(spec, getDomainClass(), cq);
-		TypedQuery<Integer> query = applyRepositoryMethodMetadata(this.em.createQuery(cq));
-		return query.setMaxResults(1).getResultList().size() == 1;
-	}
-
-	@Override
-	public long delete(Specification<T> spec) {
-
-		CriteriaBuilder builder = this.em.getCriteriaBuilder();
-		CriteriaDelete<T> delete = builder.createCriteriaDelete(getDomainClass());
-
-		if (spec != null) {
-			Predicate predicate = spec.toPredicate(delete.from(getDomainClass()), null, builder);
-
-			if (predicate != null) {
-				delete.where(predicate);
-			}
-		}
-
-		return this.em.createQuery(delete).executeUpdate();
-	}
 
 	@Override
 	public <S extends T> List<S> findAll(Example<S> example) {
@@ -571,19 +586,6 @@ public class SimpleJpaRepository<T, ID> implements JpaRepositoryImplementation<T
 		return queryFunction.apply(fluentQuery);
 	}
 
-	@Override
-	public <S extends T, R> R findBy(Specification<T> spec, Function<FetchableFluentQuery<S>, R> queryFunction) {
-
-		Assert.notNull(spec, "Specification must not be null");
-		Assert.notNull(queryFunction, "Query function must not be null");
-
-		Function<Sort, TypedQuery<T>> finder = sort -> getQuery(spec, getDomainClass(), sort);
-
-		FetchableFluentQuery<R> fluentQuery = new FetchableFluentQueryBySpecification<T, R>(spec, getDomainClass(),
-				Sort.unsorted(), null, finder, this::count, this::exists, this.em);
-
-		return queryFunction.apply((FetchableFluentQuery<S>) fluentQuery);
-	}
 
 	@Override
 	public long count() {