returnType must not be null! when working with projections

Hello, I am migrating from Spring Boot 2.2 (Spring Couchbase 3.x) to Spring Boot 2.7 (Spring Couchbase 4.x) and I am getting this exception:

java.lang.IllegalArgumentException: returnType must not be null!
	at org.springframework.util.Assert.notNull(Assert.java:201) ~[spring-core-5.3.31.jar:5.3.31]
	at org.springframework.data.couchbase.core.ExecutableFindByQueryOperationSupport$ExecutableFindByQuerySupport.as(ExecutableFindByQueryOperationSupport.java:124) ~[spring-data-couchbase-4.4.18.jar:4.4.18]
	at org.springframework.data.couchbase.repository.query.AbstractCouchbaseQuery.lambda$getExecutionToWrap$1(AbstractCouchbaseQuery.java:126) ~[spring-data-couchbase-4.4.18.jar:4.4.18]
	at org.springframework.data.couchbase.repository.query.CouchbaseQueryExecution$ResultProcessingExecution.execute(CouchbaseQueryExecution.java:84) ~[spring-data-couchbase-4.4.18.jar:4.4.18]
	at org.springframework.data.couchbase.repository.query.AbstractCouchbaseQuery.doExecute(AbstractCouchbaseQuery.java:95) ~[spring-data-couchbase-4.4.18.jar:4.4.18]
	at org.springframework.data.couchbase.repository.query.AbstractCouchbaseQueryBase.execute(AbstractCouchbaseQueryBase.java:133) ~[spring-data-couchbase-4.4.18.jar:4.4.18]
	at org.springframework.data.couchbase.repository.query.AbstractCouchbaseQueryBase.execute(AbstractCouchbaseQueryBase.java:113) ~[spring-data-couchbase-4.4.18.jar:4.4.18]
	at org.springframework.data.repository.core.support.RepositoryMethodInvoker.doInvoke(RepositoryMethodInvoker.java:137) ~[spring-data-commons-2.7.18.jar:2.7.18]
	at org.springframework.data.repository.core.support.RepositoryMethodInvoker.invoke(RepositoryMethodInvoker.java:121) ~[spring-data-commons-2.7.18.jar:2.7.18]
	at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.doInvoke(QueryExecutorMethodInterceptor.java:160) ~[spring-data-commons-2.7.18.jar:2.7.18]
	at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.invoke(QueryExecutorMethodInterceptor.java:139) ~[spring-data-commons-2.7.18.jar:2.7.18]
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.31.jar:5.3.31]
	at org.springframework.data.couchbase.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:141) ~[spring-data-couchbase-4.4.18.jar:4.4.18]
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.31.jar:5.3.31]
	at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:97) ~[spring-aop-5.3.31.jar:5.3.31]
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.31.jar:5.3.31]
	at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:241) ~[spring-aop-5.3.31.jar:5.3.31]
	at com.sun.proxy.$Proxy223.getDetails(Unknown Source) ~[?:?]
	at com.example.UserController.getDetails(UserController.java:32) ~[classes/:?]

User Document:

@EqualsAndHashCode(callSuper = true)
@Document
@Data
@Builder(toBuilder = true)
@NoArgsConstructor
@AllArgsConstructor
@JsonIgnoreProperties(ignoreUnknown = true)
@Valid
public class User extends ParentUser {
    private String firstName;
    private String lastName;
    private String address;
    private boolean isTest;
}

Projection Interface:

public final class Projections {

    @Projection(name = "names", types = {User.class})
    interface Names {
        String getFirstName();
        String getLastName();
    }
}

User Repository

public interface UserRepository extends PagingAndSortingRepository<User, String> { 

	    @Query("""
            #{#n1ql.selectEntity} WHERE #{#n1ql.filter}
            AND isTest = true
            """
    )
    List<Projections.Names> getDetails(@Param("isTest") boolean isTest);

}

User Controller

@RestController
@RequestMapping(value = "/users")
@RequiredArgsConstructor
public class UserController {
    private final UserRepository repository;

    @GetMapping(value = {"/find/test"}, produces = APPLICATION_JSON_VALUE)
    public Projections.Names getDetails(@RequestParam("isTest") final boolean isTest) {
        return repository.getDetails(isTest);
    }

Can projections still be used?

Start with ExecutableFindByQueryOperationSupport.as and AbstractCouchbaseQuery, using the provided UserRepository query and Projections.Names projection as the reproduction. Trace how the repository method's List<Projections.Names> return type is processed, then verify the behavior with the supplied controller call. Done means establishing whether interface projections are supported in this version and documenting or correcting the resulting behavior.