HHH-18658 Inner join prevents finding an entity instance referencing an empty map

hibernate-core/src/main/java/org/hibernate/metamodel/mapping/internal/PluralAttributeMappingImpl.java

@@ -947,7 +947,7 @@ public class PluralAttributeMappingImpl
 					tableGroup,
 					null,
 					sqlAliasBase,
-					SqlAstJoinType.INNER,
+					joinType,
 					fetched,
 					false,
 					creationState

hibernate-core/src/test/java/org/hibernate/orm/test/jpa/EmptyMapTest.java

@@ -0,0 +1,102 @@
+/*
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.orm.test.jpa;
+
+import jakarta.persistence.CascadeType;
+import jakarta.persistence.Entity;
+import jakarta.persistence.FetchType;
+import jakarta.persistence.GeneratedValue;
+import jakarta.persistence.Id;
+import jakarta.persistence.JoinColumn;
+import jakarta.persistence.ManyToOne;
+import jakarta.persistence.MapKeyJoinColumn;
+import jakarta.persistence.OneToMany;
+import jakarta.persistence.OneToOne;
+import jakarta.persistence.Table;
+import org.hibernate.testing.orm.junit.EntityManagerFactoryScope;
+import org.hibernate.testing.orm.junit.JiraKey;
+import org.hibernate.testing.orm.junit.Jpa;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Réda Housni Alaoui
+ */
+@Jpa(annotatedClasses = {EmptyMapTest.User.class, EmptyMapTest.Identity.class, EmptyMapTest.UserIdentity.class})
+public class EmptyMapTest {
+
+	@BeforeEach
+	public void setupData(EntityManagerFactoryScope scope) {
+		scope.inTransaction( em -> em.persist( new User( 1 ) ) );
+	}
+
+	@AfterEach
+	public void cleanupData(EntityManagerFactoryScope scope) {
+		scope.inTransaction(em -> em.createQuery( "delete from User u" ).executeUpdate() );
+	}
+
+	@Test
+	@JiraKey(value = "HHH-18658")
+	public void test(EntityManagerFactoryScope scope) {
+		scope.inTransaction( em -> {
+			assertThat( em.find( User.class, 1 ) ).isNotNull();
+		} );
+	}
+
+	@Entity(name = "User")
+	@Table(name = "user_tbl")
+	public static class User {
+		@Id
+		private int id;
+		private String name;
+
+		@OneToMany(
+				mappedBy = "user",
+				fetch = FetchType.EAGER,
+				cascade = CascadeType.ALL,
+				orphanRemoval = true)
+		@MapKeyJoinColumn
+		private final Map<Identity, UserIdentity> userIdentityByIdentity = new HashMap<>();
+
+		public User() {
+		}
+
+		public User(int id) {
+			this.id = id;
+		}
+	}
+
+	@Entity(name = "Identity")
+	@Table(name = "identity_tbl")
+	public static class Identity {
+		@Id
+		@GeneratedValue
+		private int id;
+		private String name;
+	}
+
+	@Entity(name = "UserIdentity")
+	@Table(name = "user_identity_tbl")
+	public static class UserIdentity {
+		@Id
+		@GeneratedValue
+		private int id;
+
+		@ManyToOne(fetch = FetchType.LAZY)
+		@JoinColumn(nullable = false, updatable = false)
+		private User user;
+
+		@OneToOne(fetch = FetchType.EAGER)
+		@JoinColumn(nullable = false, updatable = false)
+		private Identity identity;
+	}
+
+}