Fix potential NullPointerException in JpaQueryCreator.

With the commit for GH-2363, we introduced an unguarded call to ReturnedType.getTypeToRead(), which could return null under certain conditions. Unfortunately Spring Data JPA dod not contain a test case that triggered that scenario.

This commit switches to ReturnedType.getReturnedType() which is non-nullable and lets us inspect the calls results for interfaces, which we need to create the JPA query properly.

Fixes GH-2408

Author: odrotbohm

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

@@ -164,7 +164,7 @@ protected CriteriaQuery<? extends Object> complete(@Nullable Predicate predicate
 				selections.add(toExpressionRecursively(root, path, true).alias(property));
 			}
 
-			Class<?> typeToRead = returnedType.getTypeToRead();
+			Class<?> typeToRead = returnedType.getReturnedType();
 
 			query = typeToRead.isInterface()
 					? query.multiselect(selections)

spring-data-jpa/src/test/java/org/springframework/data/jpa/repository/UserRepositoryTests.java

@@ -2630,6 +2630,14 @@ void readsDtoProjections() {
 		assertThat(repository.findAllDtoProjectedBy()).hasSize(4);
 	}
 
+	@Test // GH-2408, GH-2363
+	void readsDerivedInterfaceProjections() {
+
+		flushTestUsers();
+
+		assertThat(repository.findAllInterfaceProjectedBy()).hasSize(4);
+	}
+
 	private Page<User> executeSpecWithSort(Sort sort) {
 
 		flushTestUsers();

spring-data-jpa/src/test/java/org/springframework/data/jpa/repository/sample/UserRepository.java

@@ -614,6 +614,9 @@ Page<User> findAllOrderedBySpecialNameMultipleParams(@Param("name") String name,
 	// #2363
 	List<NameOnlyDto> findAllDtoProjectedBy();
 
+	// GH-2408
+	List<NameOnly> findAllInterfaceProjectedBy();
+
 	interface RolesAndFirstname {
 
 		String getFirstname();